Building an artificer

[Ipuntmidgets]

I am a player that is only used to low level campaigns
something wierd is that one of the low level campaigns that we are in just got to level 17 in a hurry and I don't know how to build my artificer.
My DM is being nice and saying that i can use each level of xp that i skipped over because we are all taking a year to level and i went from level 9 to 17 because my party downed a few dragons while i was gone and i wasnt there to help.
currently i have a cheapaficer build making all of my items cost 75% less (magical artisan on all item creation feats)
25% less (Extraordinary, Exceptional, and Legendary Artisan stacking multiplicatively)
and various bonuses to cheapen the costs through making them artificer only and having a high diplomacy and such
basically my items are very cheap. I have never made it past level 12 and do not know what to build after level 12 as a player.
any suggestions would be very helpful.

[Petrocorus]

What kind of build do you have by now? Beside making items cheap.
What role do you fill in combat?

Besides, by RAW, i think you cannot stack all those artisan feats to lower item cost below 75%

[Ipuntmidgets]

all the feats stack because magical artisan reduces base price and normally how extraordinary and all those feats read it would be a price reduction of 100% but i refuse to do that so we just go with multiplicative stacking.
i fill the role of wizard because the party doesn't really have one.
I make items really cheap so i just make a lot of scrolls and I get a lot of level 1-3 spells making me hard utility.
I was a little lacking in combat because my only combat spell was an at will explosive rune which takes time and prep to win combat with.
I mostly fill the role of utility with scrolls, but i want to fill more of a powerhouse roll where i can make things that will go through encounters.
I want to turn into batman basically.
The party doesn't really use me because i focus primarily on myself and it burns my xp really hard.
i've garnered 1k xp extra from 5-9. Though I am told that i am not able to use that xp

[Pandyman]

In all technicality, magical artisan is a 25% decrease in the cost of an item's base price when figuring out the cost of exp and gold. "When determining your cost in XP and raw materials for creating items with this feat, multiply the base price by 75%." When you multiply the base price by .75, it causes the initial price to decrease by 25%, which obviously comes before dividing it by half and doing all that nifty other artisan stuff. And stacking multiplicatively will also make the price to craft much higher than it is right now. The biggest Raw abuse you can do is take some of these feats multiple times. The multiplicative stacking will hurt you though. If you are going to take multiples of the same feat, make sure you only do it with the ones that have no clause restricting the number of times you take it.

Just another note. Magical Artisan needs to be taken for every crafting feat you want to apply it to, so it does require you to decide which crafting to focus on. Legendary and extraordinary artisan stack for a 25% decrease to gold or exp each time you take them. Pre-errata you can stack them for free items. Post errata limits you from stacking the same artisan feats.

Also, D&D is supposed to be fun for everyone. Help the people that are going to fall behind like your melee and whatnot. You can pretty much glide ahead of the party so easily, but that shouldn't be what you're worried about. You should be boosting everyone up with your crafting, almost like a better bard. After you fix the cost of item creation stuff though, I'll be glad to help with any fascinating ideas you might have. ;)

[Suddo]

Here's your homework. Read the following works:

The Complete Cost Reduction Handbook by Bastian with PlzBreakMyCampaign's help (http://brilliantgameologists.com/boards/index.php?topic=7274.0) (many of the ideas in this work may not be shared by your DM consult your DM before attempting too many of these tricks)
XP is a River Thesis (http://community.wizards.com/go/thread/view/75882/19872242/Experience_is_a_River)
List of Necessary Magic Items (http://www.giantitp.com/forums/showthread.php?t=187851)

That should set you on the right track.

If you want to be batman you will probably be hording and buffing. You should focus on the other people in your party for combat and make sure out of combat things run smoothly.

Beyond that just break the wealth by level for all your party members. If they want something fancy there is no reason you shouldn't just make it except for a time limitation.