Depending on how many 8x12 are you talking about.
If you need to print hundreds of them, why not use your 3880 to print it?
You are providing "fine art printing services", not a 1 hr photo lab print.
If someone asks me to do it, I will just ask him to go to walgreen.
If someone who owns a super busy studio and wants to outsource the printing to me, and I'm sure he can feed me well, I will buy a dry lab machine.
Otherwise, why bother.
You can get 13 x 19 paper and chop them up with a table top paper cutter and use them on your 3880
If you have a medium client base who are looking for cheaper prints, get another 3880 and run 3rd party ink.
Inkjetmall makes very good Dye ink, that should fit your budget.
aaron