You guys should at least try a
recharge kit (link) that can be found at any auto parts store before getting bent over by a shop. A kit is about $30. You're mostly paying for the hose & attached gauge. A can of R134A is fairly inexpensive alone. The gauge will tell you what level you're at and how much too add if low.
The shrader valve is on the right side (drivers side) of the engine when you're looking at it.
