Although I don’t like my Scania R480. , for many reasons, it has been extremely reliable, and has hardly cost me anything in a year and a half apart from a nox sensor a week or two back. £500, FFS.
If I were you, I’d be very nervous of a v4 Volvo at that age and money. They go very well and are not too bad on fuel, but I know people who have had an awful lot of expense and downtime with them.
Scania 450 is the way I would go, unless you can lay hands on a 490, which by all reports are very good, but on that budget, I think it might be hard enough to find a 450 with less miles than the space shuttle on it.