About £30-£40 for the 32X. The games vary - £5-£10 for the common titles, but the rarer ones like Knuckles, Kolibri and T-Mek can break £100.
Check to see if the GameGear works first - a lot of them have packed up due to the capacitors inside going bad. They can go for £20-£30 boxed too.
The capacitor issues are fairly easy to fix though.