as a mechanic that has done a few boat engines for hire, I dont think the price is too far out of line... but that depends on if the boat is in the mechanics yard, if the mechanic is traveling to the boat, or if the customer brings the engine in on a pallet...
anyone in business doing a job for hire has to account for their time, and it goes both ways... if the potential customer wants an accounting for every hour he has to pay for, the mechanic wants paid for for every hour he has into doing the job correctly.
when one considers the time it takes for the mechanic to leave his shop, and travel to the boat, then remove the engine, and get it off the boat and up the dock to his vehicle, and travel back to his shop... then disassemble the engine, clean it all up and order and pay for new parts, have the machine work done, install new parts and reassemble... then take it all back down to the boat, install the motor, probably have to fiddle with the motor mounts to set it up correctly, maybe replace some exhaust components, and then test run it all after the engine and the boat has all been connected back together properly.... 5000 doesnt seem too bad of an estimate.
I will agree that if an owner wants to do it all themselves, there is a huge savings, as long as they dont try to take a shortcut and miss something critical that causes the engine to fail...
and most owners that have done it themselves have not kept time of every hour they spent on the doing it, from the very start to the very end after the test run has been finished...
if one brings the boat into the mechanics yard, then there is the travel time savings to the marina, BUT, tools are still going to have to be carried to the boat, and the engine still needs to be removed.
if the customer were to remove the motor and bring it in on a pallet, which im sure is the preferred way by any mechanic, it will be the most cost effective for everyone, providing the customer gets the engine set up correctly during the re-installation process....
average hourly cost for a mechanic $85
parts cost for that engine approx $800, depending on how hard you shop prices, which takes time, no matter who does it..
then take into account that any good mechanic will give an estimate that is a bit high, because AFTER the job is complete, its always good to be able to tell the customer that the job was completed within the estimated cost, and sometimes a bit less...
which is a huge contrast to those mechanics that give a lowball estimate in an attempt to get the job... then when the job is complete he has to add on another grand or two over the estimate just to cover his costs.... and the customer is held hostage until they either pay or the court decides...
its simple economics... if you cant or dont want to do it yourself, you have to hire it done, and the lowball bidder is very, very rarely the most cost effective person to hire for the job.
for the record, I just did twin 318 mopar V8's in a 34' Silverton FB setting in the water at a marina... I gave an honest estimate of 5000 per engine, and I had to travel 125 miles one way to get there.
I removed, rebuilt (machine work was very necessary) and took them back to the boat, reinstalled and tuned/ran them...
after it was all done, there was no excess profit... I estimated 1 day to remove them and 2 days to reinstall... I hit my mark on the hours, and I did all the parts and machining costs during the estimating process, so no surprises there. (I knew what machining was needed because the owner took one of the engines apart in the engine bay, so I seen the damage... exhaust manifold failure and saltwater setting in the cylinders)
so how are you planning to present the "rebuild" job to the mechanic, and what part of it are you going to do yourself?...