Sadly, USPS Priority Mail rates are just crazy, and have been for some time, even for domestic shipping.
You might get lucky and get someone to put it in a small box for you, which should run a little less.
Otherwise, club and/or group buys seem to be the only answer to this.
Which model of MGB are you having printed, and any chance you are on the West Coast, since I might be interested in one or more MGBs as well, if they are the right model.
I'm interested in the neat looking little, BPB MGBs (early to mid-war model, up until 1943/1944, IIRC), or BPB MGB/MTBs (1944 to the end of the war, IIRC, but could also be late 1943, I suppose) with the whale-back cockpit, though I'd be interested in the shorter style, late MTB cockpit too.
I'd like at least a 2 Pdr. on the foredeck, and a 6 Pdr. would be neat too (even better if they can be swapped out with magnets).
I'm interested in 2 – 4 of each, if available.