Like all things,
That would depend on year/modle/hours/condition/anyknown history?
But ultimately it depends on how much its worth to you!
The best advice is too get the best motor you can afford and take someone who knows with you, buy a motor that you know the history of, or from a recommended source, and unless your really sure stay clear of anything on ebay!
Just remember you canít push a boat to the side of the road!