The best you can afford from any reputable maker.
The best one you can afford that was designed for 22LR rifles.
I BUY AND SELL THESE ,ABOUT $100 IF IN REAL GOOD CONDITION
you will have to have a gunsmith check it to be sure.
175 USD
175 USD
eBay would be a good place to start
22LR
There are no "good" scopes for that price. If you haven't the money to buy a decent scope, odds are you don't need one.
Gun shop, gun show
Yes it is.
Only if the airgun has a scope rail designed into the gun. You will also need an airgun scope not a firearms scope.
"Best" depends on what you want to use it for. Hunting squirrels you will need a different scope than you would use for 100 meter benchrest shooting. Like most things, you will get what you pay for. The higher dollar scope is likely to be brighter, not fog up, hold a zero, and be more durable.