Airbag replacement 2000 V40?

[olddaddy]

Our 2000 V40 airbag light came on for no apparent reason and stayed on. The dealer charged us $100 to tell us we need to replace the passenger side airbag mounted in the seat. The note said, "internal fault in sps bag right front seat, fault code SRS-0087. They want $700 to fix it.......I am pretty capable mechanically and wondered if this is something I can do? And wondered if there is a sensor, or module that can be replaced or does the entire airbag have to be changed out? Can I buy an aftermarket or used airbag? We want to keep the car safe, and maybe $700 is a fair price, but I'd like to know what other owners have done, or what you think about it.

[MadeInJapan]

Before doing any of this look for a connector under the seat disconnected or a frayed wire....these hardly ever go bad on other Volvo's.