I currently have 4 units in use, all of which are absolutely satisfactory for my purposes, and not too expensive:
1) Alesis Microverb III - connected to my 6 channel Ibanez mixer, which I mainly use as a microphone preamp for recording vocals, sax, trombone, and hand percussion such as djembe, tablas, cajon, etc. Should be around $100.
2) Alesis Nanoverb - in my synth section, paid €50. I have built a little switchbox with 4 inputs for my synths and the theremin, and a switchable passive effects loop linking an Ibanez analog chorus pedal and the Nanoverb if I want to.
3) Furman RV-1 spring reverb - in my guitar setup. Might be over $200 today, there is one on ebay.com with $225 starting bid.
4) Vesta Fire DIG410 digital delay - also in my guitar setup (there are eBay offers asking $300+, though