I have a couple of 545i backs, a 405 and a 455. Asking $40 for each or $120 for the lot. Please add $10 for shipping in either case. I have 100% positive feedback on fredmiranda, Astromart, Audiogon and eBay.
Your 405 back is worth close to $200. The others are icing on the cake.
It's not that much... The pa145 new in box from japan maybe, but usually it and the 405 used can be anywhere from $60 to $150. That said the back is awesome to have. If the first sale doesn't go through id love to have an extra!