I retro fitted a PT unit to mine. The (gubbed) unit itself cost me £100, the repair kit another £50 odd, then added a couple of evenings of foul language & sheared bolts to remove the old manual one. I'd say that's a fair price, specally if the PT gubbins is new! (you'll also need extra wiring to the helm, and a mod to add the switch to the "go lever")
Pol does have a call tho'. If you can get a quote for a P/X or can punt your current engine there is a good chance at that kind of HP that you may be able to do it for less than the upgrade, and / or you get a new engine. Alternative view is if you do the upgrade, you know the history of the rest of the engine.....
Worth checking out both options tho'.