Tim, on the serious side..Why not look for a used Roland E-600[it has a touch screen, a mic input and harmonizer..]. You should be able to find one under $500[and can get your money back out of it again].
Another , maybe a PSR2100[ spend under $500 though].It may be harder to resale..

A Farfisa G7 in the $300-$400 range[also a harmonizer and mic input.].
New.. maybe a Roland GW-7[you really have to deal to get one near $500..probably $575..

How about soft synth and OMB world with a $250 controller..You will have to get your feet wet, sooner or later..