Rebuild engine or buy rebuilt?

I purchased a used 2020 Raptor 700 for $5.2k, had some broken plastics due to being flipped but it ran good. Before I bought it asked the guy when is the last time he did an oil change and he said “it could probably use one by now”. I changed the oil like I always do when buying a used ATV. Ran 15w-40 at first but it gave me a small knock after a few hours of use, so I changed it 20w-50 synthetic and the knock went away, didn’t think much of it and rode it for about 10 hours, no issues. I noticed the quad was taking too long to start (10-15 sec) so I adjusted the valves and it was knocking once again. Took it to a shop and they said there was metal in the filter and oil and it’s most likely the crank bearings going bad but they would need to take it apart and charge at least ~$400 to confirm.

My question is, should I find someone to rebuild my engine with the a new crankcase and bearings (case is $600 alone) and HOPE the case is still in shape? Or, try to find a rebuilt engine and swap it out? Does anyone know who on here sells rebuilt engines?

Video after valve adjustments

Any input would be appreciated, thanks!