- Do you want to save loops into memory and call them back later? Export to computer?
- Do you need to switch between different loops, for instance to follow song form?
- Do you need to syncronize your loops between themselves or with other gear? Master or slave?
- Do you want to use pre-recorded material on your looper?
- Do you care about feedback control?
- Undo / redo?
- Control with feet or hands?
- Have you considered delays instead of loopers?
- Do you need, time or pitch shifting? Rate shifting?
- Do you need reverse?
- Do you need a looper that runs on batteries?
- Do you want to control your looper with MIDI?
Not knowing anything else about your specific looping needs, for that price-range I imagine people will likely recommend a DL4, a DD-20, Vox looper or a LP2. I've had a lot a fun with the LP2 and the DD-20 and I know a lot of folks who swear by the DL4. You could easily find a store that retails the DD-20 and DL4 (perhaps also the Vox) in your area, so go try them out.
I'm not sure why you'd need a harmonizer if you're playing a synth... couldn't you just program the synth to give you two voices when you want them? In any case, if you want both a looper and a harmonizer together, you'll need something like a TC-Helicon Voice Live 2. It will cost you more than you want to spend...
