Because of some stupid OCD-like curiosity about how to price metamagic rods for those not listed in certain books, I did some number crunching, and found the formulae.
Lesser MM rod prices
3000 ( 3rd CL * (1x2-1))
9000 ( 3rd CL * (2x2-1))
14000 ( 3rd CL * (3x2-1))-1000**
26000*( 3rd CL * (4x2-1))-1000**
Normal MM rod prices
11000 (11th CL * (1x2-1)
32500 (11th CL * (2x2-1))-500**
54000 (11th CL * (3x2-1))-1000**
75500 (11th CL * (4x2-1))-1500**
Greater MM rod prices
24500 (24th CL * (1x2-1))+500**
73000 (24th CL * (2x2-1))+1000**
121500*(24th CL * (3x2-1))+1500**
170000 (24th CL * (4x2-1))+2000**
* - these values were adjusted to fit the formula, but seem to follow the splatbooks with some variation.***
** - I found the pattern, but not the reason for these adjustments***
*** - The DMG states that pregenerated magic items sometimes have different price than their 7-33 calculated price for balance purposes
Why CL 3, 11, and 24? Because that's the formula they wanted to use. What formula? Lesser: 0+(1x2)=2, 2nd level spells are at 3rd level for Vancists. Normal: 2+(2x2)=6, 6th level spells are at 11th level for Vancists. Greater: 6+(3x2)=12, 12th level spells are at 24th level for Vancists (those whom take the Improved spell capacity for their level 21st, 24th, and class bonus feat at 23(or 24 for druids.)) (Or maybe it's because 3+8=11 11+8+5=19+5=24, and you're expected to get 5 levels of archmage between 11 and 17 for this to make sense, but I find that less likely.)
If the item is priced at 24th caster level, then why can you make/buy it in a non-epic campaign? Because its price is under 200,000g, which defines it as a non-epic item (splatbooks sometimes violate the 200,000g barrier, but not by much, and I think the reasoning is that 25th caster level is the max caster level at 20th level, so non-epic prices can go up to 250,000?)
So, you want to make an lesser epic metamagic rod capable of enhancing spells of epic characters up to 12th spell slot level, what CL do you use as the base for price calculation?
By the formula, it's at a spellslot of 12+(4x2)=20. Assuming you're a wizard or cleric, that means: [13:26CL, 14:27CL, 15:29CL, 16:30CL, 17:32CL, 18:33CL, 19:35CL,] 20:36CL
That means it's price progression is going to be something like:
36000+x (36th CL * (1x2-1))+x
108000+x (36th CL * (2x2-1))+x
180000+x (36th CL * (3x2-1))+x
252000+x (36th CL * (4x2-1))+x
The pattern, or lack thereof of what X is from lesser to normal to greater lets the DM choose what X would be. My suggestion is that it's somewhere between 200,000g to 250,000g, or multiply the price of each of those items by 10 and remove x, like what happens when anything with an enhancement bonus (weapons, armor, stat boosting wonderous magic items) becomes epic. Also, I'm not going to do the full tables, but epic MM rods use 30:51CL for pricing, and greater epic MM rods (which I would either say is the ultimate cap either at 18 spell level or with no max spell level) 42:69CL.
Using above formulas expanded down to the 6th line, we get the price for the most wanted rod by CoDzillas and arcanists alike.
Persistant MM rod
lesser: 31,000, normal: 118,500, greater: [267,000]

What thinks ye olde playgrounde?