Try loads on would be my first recommendation - just to see how they fit. Price does not guarantee comfort so it's worth trying pairs on just to find out what you like and what to look for.
Wrap around style (not necessarily full-on) is a must imho, not for looks or stream-lining but for eye protection. Not just insects but stuff in the air. Also, air flow around the sides of glasses can cause eye watering - wrap around reduces that flow.
If you're thinking of interchangeable lens then don't go overboard; clear is essential, then amber and dark (sun). Any more than that is 'nice' but not necessary, imho. Or you could consider having a few pair of specs with different lenses. That's what I do. I use interchangeable lenses for clear and amber but have separate sun specs as well. Personally, I prefer to swap glasses than change lenses.
You don't need to spend a lot for something that works. You'll find safety specs on
ebay for a fiver that'll do the job (if they fit comfortably!) Have a look in TK Maxx if you have one near you. Or
Decathlon - they have a very good range of affordable specs. And there's always Aldi and Lidl, when they have their cycling stuff.
My last bit of advice is to not spend more than you can tolerate losing! Glasses are the kind of thing that get lost or broken easily (at least ime). If I had a pair of £100 brand x specs, paranoia would get the better of me and I'd never wear them!