You’re right on the edge of commercial vs consumer shipping.
If you’re an individual... you’re best bet here is probably still FedEx. Their charging is based on the overall size of each box, with little concern on weight. If you have a walmart nearby that’s open late or 24 hours head over to one real late 11pm-1am and ask a stock worker for boxes. They tend to be as generous as you can carry on giving them up.
Keep them square and rectangular and you can ship a LOT of weight for little money. I can get over 100lbs out for under $60 using smaller boxes.
On the other hand if you’re near a larger city you can usually get a single gayloard (a wood or plastic pallet with very thick cardboard walls attached to it) for around $50. In that case what’s know as LTL (less than truck-load) shipping is a good option as well. You can find many carriers listed either in freight or logistics.
Just make sure they are aware you don’t have a forklift.
If you read through the
business/generic threads there’s a few LTL haulers offering discounted rates to boardsort users.
300lbs of motherboards will run between $285-$1080 based on today’s rates depending on the size and sort.
If you go the gayloard route use “flats” (cut cardboard insert) to separate classes in layers.