I use a TC Helicon Harmony Singer pedal:
http://www.tc-helicon.com/en/products/harmony-singer-2/
Well under $300. Very basic and easy to use. Good reverb, auto EQ and natural sounding harmonies. No pitch correction though if that's something you want/need.
FWIW I owned a Digitech vocal harmonizer which I found to be less natural sounding and not as straight forward to use.