I’d say you need about $250 for a decent graphics tablet, but there are many cheaper ones, especially if you don’t mind getting a refurbished graphics tablet.
Here is what they have at TigerDirect
(Link)I use an Adesso CyberTablet 12000, about five years old now and it still works great, though I have heard horror stories from some other people,
It cost about $200 back then, and I managed to hit a sale so I got mine for $150.