By computerized do you mean you have something you want to use that will need to be scanned in and turned into a graphic image? Or taking the idea and finding suitable clip art OR having the designer draw something in a graphics program similar from scratch?
The pricing really depends on which approach you need. Although scanning in and cleaning up is about as much effort as doing something from scratch. Most WAHM designers charge anywhere between $20 hour and up - usually in the $40 and up range.
I love websavvymama's work. I also love and have used LauraJane from chickenscratchslings.com, she was so fantastic to work with, and so talented. You can see my page at www.booby911.com to see her work.