Welcome back

The A1000 tends to be rarer and more expensive. They're also pretty limited in terms of expandability.
So given your detached-keyboard requirement, I recommend a 2000 as a good way to get back into Amiga games. It'll run pretty much all of the classics, it's cheap, and it's expandable enough to grow with you as your needs change - such as adding a hard drive, accelerator and RAM, and using WHDLoad.
(
WHDLoad is a fantastic support program that allows you to run many/most floppy-only games from your hard drive. It requires a little more horsepower than when playing direct from floppies.)
For a basic, unexpanded A2000, I'd pay no more than $100. With a SCSI card and hard drive, maybe $150. If there's an accelerator installed (most likely a 68030), you're probably looking at $250 or more.
Things to be aware of when purchasing: make sure the battery hasn't leaked, and make sure it has the Kickstart version you want. Version 1.3 will be best for playing from floppies, but you'll need 2.0 or higher for WHDLoad and most other non-gaming tasks.