you only need a few pounds pressure to run your carbs. You could check with your local auto parts store & see if they have a cheaper low pressure electric pump & wire it into your ignition fuse block. Just leave the mechanical one in place with the hoses removed & re routed to your electric one.
speaking of using an electric pump, you mention to leave the old one in place? I was wondering about that. Would it be a potential problem, the old mechanical pump, still moving, up/down, up/down, with no fluids to either cool or lubricate, could it sieze in any way that might cause some sort of damage? I don't know if its some sort of cam shaft that drives it or what, but kind of thinking that it should be removed and the hole plugged against rain/dirt, etc.
Checker Auto out here in AZ has two electric pumps in the store, one about $50, the other about $80... Been tempted to try, especially since I'm semi-questioning my existing pump.