Your best bet is ask round locally to see if someone has had a stainless exhaust built for their cars. If you fancy a few days in Ipswich (a long way from home for you) give these guys a call :
https://demandengineering.co.uk/
Very high quality work and they will build to what you want. In other words, if you want it sounding like a refugee from Santa Pod, they'll make it sound like that. If you want it to sound standard, they can make it like that too. If you want it a little sportier than standard without a drone or intrusion, they can build it like that too.
Worth noting that almost all stainless systems give a characteristic rasp, no getting away from it as it's a characteristic of stainless steel.
In terms of price, you're probably looking at around the £400 mark, give or take a bit but a system from Volvo will cost similar, a Bosal mild steel system will be similar too. You can get cheaper systems - loads on ebay but i don't think there are any off the shelf stainless systems any more.
All depends how much you want to spend, how long you're keeping the car and so on. Also worth noting that you can't just buy any Volvo 740 system and expect it to fit, there are several different systems depending on year, model, transmission, Lambda or not so you've got some homework to do before you even start.
