The tool you need is pretty inexpensive (under $10.00) so if you're going to continue using this freewheel, It's worth buying. Otherwise you can let the LBS do it - they should charge $5.00 or less. BTW- freewheels are require a decent amount of torque to remove because they're tightened by chain tension, so are on as tight as when you stood on the pedals climbing a hill.

One consideration whether to purchase the tool, or not is what happens afterward. If you're reusing the same freewheel, or replacing it with a similar model, the tool will pay for itself. But if replacing it with a different brand freewheel, pass on the tool because it won't be usable next time, and consider buying the tool matching the new freewheel. (there are 7-8 different types)

If the freewheel is toast and you're replacing it anyway, you can use a drift punch to spin off the front plate and the freewheel will fall apart allowing you to clamp the body in a vice and turn it off. (the front plate spins off to the right)