i'd be very interested for you to reveal the source of the PA-145 for fresh film for that price
Patience! Where were you four days ago?
A quick [advanced] search on the auction site shows two backs (a pair), just sold for $50 USD each, w/$8 shipping.
I bought one, not too long ago right here in the APUG classifieds for $55 USD. (Can't remember the shipping cost).

From a completed *Bay Auction-25FEB w/only one bidder: Item # 200900867284

*Note: To be specific, these were the 'Polaroid' 550 backs, not the 'Fuji' PA-145 backs. At this particular, point-and-time,
(regarding instant pack film photography equipment), the difference between the two backs is basically moot.
They both get the job done!