I have a 98 V70 and added the third seat. The cost varies dramatically by the year. The 98 and 99 will take the same seat as the older 850. This is significant as you can buy the seat and all hardware new for about $300 US; otherwise, you are looking at close tp $1000 for the seat.

The seat installation is not exactly straightforward. I had it done at a local body shop. It took them four hours. If you are very handy you may be able to tackle it yourself, but beware it is a very tight fit and involves cutting with patterns.

Once installed the seat itself works well, but it is only suitable to kids betweenn 55 and 90 lbs. It fits my seven year old great now, but my 12 year old daughter is too big to sit back there now.

All things being equal, it is worh an extra $1000 with the saet already in. So if you are getting a deal on a car without just factor in the extra grand for coparison to determine whether it is still a good deal.