I bought a used Kowa 77 mm Flourite lense spotting scope years ago.I got a deal.
Amazing scope.
I can count on seeing .223 holes in an orange on white target at 300 yds nearly always.Under just the right conditions,I haveseen .30 cal holes in the black at 500 yds.,but that's a rare day.Its incredible for spotting and watching a deer two ridges away.
BUT,here are some important things to consider.
1) An eyepiece for that scope will about use up your $500 budget
2)I live at about 5000 feet in a dry climate. A big "optical factor" is the air between you and your object. Humidity,mirage,dust,pollen, smoke,haze and even altitude(maybe) will make a difference.
3) Optical quality and objective lens size make a difference.There are tradeoffs. A 60 mm lense won't "see" as well as a 82 mm lens,all else equal.
4) More magnification only goes so far.With my 77mm lense,about 45X is about as much as I get benefit from. That's only about a 1.5 mm exit pupil.
I narrow my field of view going to 60X,and the image is bigger,but I don't get better resolution.
5) Stability is everything!. If your scope is moving,via wind or whatever,at least my eye cannot see diddly.
I sometimes use a bunny ear benchrest bag. That's steady. Just don't mix sand with your scope.A really good tripod is a good investment.
Being realistic? If you have $500 to spend,unless you get a deal on something used, between the scope body,eyepiece,and tripod....I think I'd focus on the best binocularsI could find.
If you go with a compact spotting scope...50 or 60 mm,understand how exit pupils and magnification are related.In really good light,about a 2mm exit pupil matches your eye's exit pupil. You won't see much advantage in more than 30X for a 60mm lens,or 25X for a 50MM lens,and 20X will be better on a cloudy day.
A 20 to 60 zoom is not going to be much benefit on a 60 mm scope.
Without putting anything else down,I'm a KOWA fan.No personal experience,but I suspect Vortec may have merit.
IF you wear glasses,do consider LER eyepieces,and eye relief.Look for around 20mm eye relief,