Yeah man you might want to look and think long term. I know money might be an issue but I would highly recommend you getting a Mac Pro. You could get a quad core 2.66 referb from apple.com for 2K. That way when your studio grows and you need more power, UAD card or SSL duende PCIe or whatever else comes out next you can easily expand and keep up.
iMacs and mac books are consumer level
Mac Pro's are professional grade computers
Don't drop $1500 on a computer then in a year and a half find out that you need more
..... I've been there. Try to stack ya bread and get somthing that will last!
My 2 cents