A good spring/piston rifle isn't something you want to use to shoo nuisance deer, as they have 'nough oomph to do some damage. I've swatted starlings out to 90 yards with mine and taken home roosting bandtail pigeons and squirrels with ease at 30.

Like most things in life, extra $$ will get you something that pushes a quality pellet through a match grade bore at a utilitarian velocity with a negligible standard deviation which equates to accuracy worthy of some good glass to launch same with precision. Scopes need to be specific to air rifles as the vibration of a s/p can damage less hearty varieties and parallax needs accounting.

With care, a quality rifle will also provide enjoyment for several generations hence. Once purchased, they are both inexpensive and a joy to shoot at either paper or vermin. The Germans make some serious break-barrel spring/piston offerings. Mine is a Feinwerkbau 124 in .177 that is well over 30 years old and still splatters flies wandering across a target at 20 yards. The newer pre-charged bottle guns are intriguing but have their quirks. Check out Beeman and other airgun sites. The only difference betwixt men and boys....

For your deer, a paintball marker might do the trick, and put a grin on your face. An old Tippmann 98 is easily cleaned-up and powered with compressed air or CO2. Deer getting repeatedly tie-died would provide entertainment for your flowers....