Assuming you mean floor type platform jack, Harbor Freight has one on sale now for $70 or $80. If you're not familiar with HF, they deal almost totally in "asian" imported goods. The quality varies greatly, but most everything works, at least for occasional use.
I've bought one of the jacks, but it's still in the box so I can't comment on the quality/suitability.
They have two websites. harborfreight.com and harborfreightusa.com (I think). One will do online sales and the other only describes the items and refers you to a b&m store, or so I was told by the store guy.
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