You don’t just hire anybody to cut out a truss rod slot on a Moollon bass that doesn’t have one.
Considering all the labor involved, a luthier/tech who is of the proper caliber to do this job right on a premium instrument is going to want at least $75-100 and probably more. There is more involved than just a router and a handshake - neck removal, pickguard removal, router template fabrication, cutting the wood and the pickguard, measuring and masking, whatever spot refinishing and/or beveling needed to make it look factory and professional, and then reassembly. This is not quick and easy.
if an inexperienced person tries to do this on a high-end premium instrument, it’s going to end up looking like a dog that lost every fight. Guaranteed. And then nobody will buy it second-hand unless you knock off hundreds from regular asking prices.
So add $75-100 to the time and expense of going to a good shop, dropping the bass off, waiting the time it takes to do the mod to a high standard, and then going back to get it. Last time I checked, YJ charges $150 for the notch as a build option. This seems to be in the realm of fair, keeping in mind it requires extra time he might not really have in light of all his outstanding orders.