Price depends on whether you stumble upon a used system cheaply or buy on eBay or elsewhere where retro computer prices have skyrocketed. On eBay, you could probably expect to pay $200+ for the system I described or individually much more to construct (i.e. $100 for bare A1200, $150+ for BlizzardIV, $80 for SCSI board, $20 for 2.5" ide drive, $15 for 12x scsi cdrom, $30 for Silversurfer/Twister board, $10 for 3Com pcmcia...not including s/h).
I've heard people have good luck putting ads in local papers offering to 'dispose/take care of' old Amiga stuff. Probably worth a 20 cent personal ad.