My 2 cents. If you plan to use the boat you buy in rivers, esp if you would classify yourself as an "unexperienced river boater" then I would buy a jet outboard. Yes, you lose 30% power or whatever it is (eg 60hp is a 40hp jet) and they do cost more to maintain. However, a jet outboard wil allow you to navigate (sometimes unexpected!) skinny water that would ground out and likely damage your prop.
A couple anecdotes: Went out wih our neighbour a couple weeks ago to try out his 17-56 Lowe Rouchneck with 60/40 Yamaha jet. The water in the Fraser was quite murky and impossible to see bottom approaching a few bars we beached on. A few times the water shallowed up suddenly and if we were running a prob I'm sure we would have drug bottom as we thought it deeper where we were.
Been out with a friend several times in the Fraser in his 14 foot SmokerCraft deep-V with 35hp Merc prop motor. Guy is a reasonably experinced boater, certainly more than me. Last year we suddenly hit shallow water (1 foot or so) going at a reasonable clip and we we lucky to not have been launched out of the boat. Propellor was damaged baddly but luckily we could limp back downstream to where we launched. Similar situations to this have happened to him before without me in the boat. He said bugger this, sold the prop motor, and now has a 30 Yamaha jet. He is much happier and says he feels much more confident with this boat in the river(s).
Misses and I are currently in the market for a river boat that we'll also use in lakes for trolling. Given that we are not experienced river boaters we are going jet power for sure.
If you are an experienced river boater and know the water well that you will be navigating then a prop outboard might be fine. If you are like me then I would pay more for the jet and piece of mind.