I have added Custom Twitter Backgrounds to my list of services here at Custom Blog Designs. If you have ordered or had a makeover done by me then the custom background is $12. If you just need the background and haven't ordered a makeover the cost is $17*. These fees include installation and custom colorization to match the background.
*The cost may be higher if graphics need to be purchased for the background.
Here are some twitter backgrounds I've done~
I am not taking any new clients at this time. Repeat clients may contact me for updates. Please note that updates are not free!!
If you are looking for a new design, I suggest you check out Etsy. There are 100s of affordable customized designs. Most offer installation for a nominal charge.