Customized magic item pricing

[Occasional Sage]

If your player wanted to make a variation on a Bag of Holding in the form of a traveling bookcase (and which can only hold books, scrolls, inscribed tablets, etc) which uses Mending on anything left inside, how much would you discount it for the sharp limitation on its usefulness?

[Nettlekid]

How does it work? Is it a full-sized bookcase that has extradimensional storage, or like a small box big enough for one book that you put more books into?

I could see it going one of two ways. Either a substantial discount, like halfway between the regular price of the Bag of Holding and an Infinite Scrollcase (which this sounds like it resembles except that this can hold larger books as well as just pieces of paper), or alternatively (to save yourself the headache of adjudication) suggest that since this item isn't really popular when compared to a Bag of Holding, the amount of cost cut from it for the niche use is balanced out by the specialized creation process used to have it accept only books, so the price is the same as for an equal-sized Bag of Holding anyway.

[Lord Vukodlak]

A traveling bookcase looks like this.
http://s3.amazonaws.com/materialicious2/images/tom-stoppards-traveling-bookcase-m.jpg?1244212232 Maybe that be Type I

A larger one looks like this
http://www.ritesofpassagetravel.com/uploads/images/content/blogs/15/traveling-bookcase.jpg

For pricing perhaps, 2,000gp for one hundred books, with the convenience of automatically drawing the book you desire. Its easily holding more weight then a type I bag of holding or a handy haversack but as it only holds books...

Alternatively instead of a traveling book case with extra dimensional space. Make it a book with extra dimensional space. In this case it can simply replace its own pages with the pages of any book contained with in.

[Occasional Sage]

Your "larger" is what I have in mind, with more depth so that shelves can fold out-and-back "infinitely".

Two k for a hundred, and an additional thousand for add-on hundreds when it needs upgrading? I'd call that reasonable.

[Debatra]

Don't forget another 1,500 for Use-Activated Mending.

You may also want to read up on the spell itself, which has its limitations (http://www.d20srd.org/srd/spells/mending.htm).

[Devronq]

I remember in second edition there was a "gem bag" of some sort that was a bag of holding that only held gems and a huge amount at that. There was also a "scroll case" of some sort that only held scrolls and papers. If ether of these items were converted to 3.x that might be a good place to start. If not the price in 2nd edition is probably not worth looking up and Im sure the gp item cost system is entirely different.

On another note id vote for 1/3 the price of a bag of holding or similar item that can hold anything but that's just my opinion as a DM. Id also give the mending effect for free i mean it aint gunna break anything and the item does have a very limited use.

[Splendor]

D&D really doesn't seem to offer discounts on items that hold only specific items. In fact they seem to charge more. Comparing the Infinite Scrollcase or Quiver of Ehlonna to a bag of holdings shows you that.

A Heward’s Handy Haversack can hold 120lbs of equipment and costs 2000gp. (16 2/3gp per lb)
Bag of Holdings 1 can hold 250lbs and costs 2500gp. (10gp/ lb)
Infinite Scrollcase only holds 50 scrolls and costs 1400gp. (maybe 250gp/lb)
Quiver of Ehlonna hold 66lbs worth of arrows/bows (mostly) for 1800gp. (27gp/Lb)

The pictures above (which I like) hold about 13 and 72 books respectively. So lets look at something that weighs maybe 15lbs (like a bag of holdings 1).

I would make it so that when the case is open the books are each held in a little shelf that can be slid or lifted out. 10 Books per shelf. 8 shelves for books for a total of 80 books. Two additional trays would also be included. The first one would be a velvet lined fitted tray that would hold ink bottles and pens (could even fit a potion in there). The second would hold an accordion folder that could hold 50 sheets of paper. Two side pouches would each accommodate a cylindrical case that could hold up to 10 maps on each side, these map cases are long (like 3') but slide easily into the 12" side pouches of the case.
80 books x 3lbs each = 240lbs
20 maps x 1/2 lb each = 10lbs
50 paper = 4lbs (?)
Ink & pens = 2-5lbs (?)
Total Weight = around 257lbs

Which is pretty close to the cost of a Bag of Holdings 1. So since D&D doesn't offer 'discounts' on items of holding I would keep the price the same at 2,500gp.
To that you wanted to add mending... Mending only affects 1lb.
You have 240lbs of books + possible scrolls + possible maps. I would say it slowly mends items placed inside it, and must be in the case for 24 hours before mending happens. Mending is cheap: 1st level caster * 1/2 level spell * 2000gp = 1000gp. And since I would say it only affects "wooden" items placed inside I'd give it a 25% discount. So +750gp?

Self Repairing Traveling Bookcase
This small 12"x12"x14" traveling bookcase is made from waterproof leather and reinforced with metal edges, corners and hinges. It has a small lock (simple) set into the side/top. When opened it reveals two small shelves; the first containing Ink & pens, the second a large folder able to hold various sheets of paper. Two small pouches on the side are empty.
However, when a command word is spoken before the case is opened 8 additional shelves can taken out of this case each holding up to 10 books. If a second command word is spoken inside each side pouch a map case can be found. In addition any paper/book product (including book bindings) that is left inside the case for more than 24 hours has the mending spell cast upon it, repairing small rips or gouges.
Weighs 15lbs and costs 3250gp.