JD kits are pretty cheap compared to most other brands (kubota is usually double) $8-1100.00 depending
I would have the head worked if it were me while it’s off. Wet liner engines are also the cheaper to build labor wise.
That said I couldn’t imagine it being done by a reputable place less than $4k.
I’ll be honest and say one thing we have to do these days that I didn’t use to worry about, every engine we build these days gets a little extra figured in for Chinese parts failures. Any engine I’ve built in the last 5 years that failed was part failure but I still have to warranty it.
If a Chinese kid gets a little off on his QC and a bearing fails, we get that bearing replaced that’s it then if it burns a crank shaft I have to buy one and then we have to buy the gaskets,fluids, filters etc and build it again.

That’s why I won’t build engines in house anymore unless they stay local. If we build one and it gets 1200 miles from home and a bearing or gasket fails it could cost me 4-5 times what I charged to build it to get it repaired or back home so I can repair it