From the photos, it does appear to be in great shape - nice bakelite agitator! $150.00 may be a bit on the high side, unless it's in fantastic shape.
If I was inspecting it, I'd check out the condition of a couple of specifics:
- the 2 wood bearings in the lower wringer frame. And the 2 attached to the upper rolls.
- the mechanism under the bottom wringer roll that diverts the drain pan/flume.
- underneath for signs of oil leakage.
- the agitator post and drive block.
- mechanism to activate the pump.
Regarding replacement parts - the wringer assembly looks to be a Lovell, and occasionally some rolls appears on ebay. Other than that, I'm not familiar with the Kelvinator brand.