Tom the 99 parts are out there cheap if you know where to look. The only stickler will be the block. The rest of the stuff can be had for a decent price if you shop around. But you will spend some coin. Keep in mind though you can build 550" with available parts and blocks which can be had very reasonably.

If it were me I would build the B1 and make it able to handle a decent shot. After all this is a backup piece right? You might be surprised how fast it can go with a 300 shot or better.