Hello and welcome

To answer your questions. Without a doubt they are highly underrated cars. They can (and frequently do) cost a bit to maintain but it's worth it. Are you used to playing with spaners? If so, get a Trade Club card by joining Autonahnstormers and it means that you can by the oil and filter for a change for around £14 as long as you buy 20L of oil at a time... Well worth it and covered here many times.
As for the car... I disagree with Webby a little. I wouldn't be looking for a low mileage car specifically

My saloon had over 177k on the clock when I sold it and was running better than my estate at 70k

Just a case of checking it has been maintained properly

And that doesn't mean a Full Vauxhall history either

Main things to allow for are Cambelt
Kit change every 40k/4 years and wishbone bushes. You also need to allow (in your budget) for a full geometry setup unless it has been done recently

Everything else (pretty much) is fixable with the guides on her and when they are running right they are a very nice drive.

Good luck with the search