You'll find it hard to find a real bargain on Ebay. Some go for not much less than full price, and that's without guarantee and database voucher.
I got mine for £200 on Ebay, which was a reasonable price I think. Had to buy a PC cable and database update. Also had to load up latest software update. Once all done. Very, very happy with it. Although at the moment the novelty hasn't worn off, and my eyes are not out the cockpit enough.
But be warned. If this is your first moving map GPS, you may find that the GPS in itself is not enough. If you are to maximise it's usefulness, you may find that some flight planning software such as NavBox ProPlan (c£75) will come into it's own. It goes like this:
Draw a line on the chart
Copy route and waypoints in flight planner on home PC
While you're at it download NOTAMs and MetForms 214 and 215
Enter wind details
Produce Plog
Upload to Pilot III
Go fly.
Such is my experience....