1999 Volvo s80 SRS light on says it needs urgent service

I was looking to buy a 1999 volvo s80 the private seller is asking for 5,495. The vehicle has 105k miles 1 open recall and was owned by two people (same family). The SRS Airbag Light came on saying that the SRS Airbag needs urgent service. I know it costs around $100 to have the computer do a check but how much would it be to repair the problem assuming the most expensive it would cost? Aside from that the vehicle also needs alignment, some upholstery touch ups, a new battery and brake lights. I was thinking of offering 4800 because of the repairs I would need to do. Do you think that is reasonable?  Thank you for answering my questions