This is an example parts list based on the work done by Johnny Lee on his PAPR design.  It's not well vetted at this time and needs thorough testing to ensure folks in different regions can bouth find the parts and use them succesfully, but gives a starting point on what it might cost to assemble your first DIY PAPR

 

Part Cost (USD $) Supplier Link
Arduino Nano  19 Amazon https://www.amazon.com/Arduino-A000005-ARDUINO-Nano/dp/B0097AU5OU
 CPAP Mask 23   Amazon https://www.amazon.com/ResMed-AirTouchTM-F20-Cushion-Large/dp/B075MQMKXP
 CPAP Hose  10  Amazon  https://www.amazon.com/RespLabs-CPAP-Hose-Premium-Tubing/dp/B07776MLBC
 Brushless DC Blower 10 Amazon https://www.amazon.com/Fugetek-Brushless-HT-07530D12-75x75x30mm-Computer/dp/B00B2ARV22
 CBRN Filter 80  MIRASafety  https://www.mirasafety.com/products/cbrn-gas-mask-filter-nbc-77-sof
 2 x 12V Battery  44  Amazon https://www.amazon.com/Tenergy-Capacity-Rechargeable-Replacement-Equipments/dp/B077Y9HNTF
 Goggles  13  Amazon https://www.amazon.com/Aegend-Swimming-Protection-Triathlon-Multiple/dp/B01LNAU866
 Faceshield  15 Amazon  https://www.amazon.com/Disposable-Resistant-Transparent-Protection-Splatter/dp/B086H6KRPZ
       
Total   215