A couple of cheap options (yes Canadian site, but I'm sure you could find something similar)
http://www.tigerdirect.ca/applicatio...&Sku=A685-0086
http://www.tigerdirect.ca/applicatio...108-33002%20CA
Not sure how good either of those are, I don't have either, but it at least gives an idea of what a 7" tablet might run you on the lower end.