If you want to get serious about it, and you want to go over 8x10, which is about where I was 2 years ago -- I might suggest the Epson R3000.
I have an R2880 -- which was the previous model to the R3000. The 3000 should a bit cheaper on ink as it has larger tanks on the cartridges. It goes up to 13" width and uses Pigment-Based Inks, which are archival quality.
You are likely looking at around $600 with possible rebates, but that is just a guess. My 2880 was $699 2 years ago and with a $200 rebate ended up about $499.
I would wait and see what Ernesto (esantos) says -- he was the one who recommended the 2880 to me.