If only one side is making grinding noises, it is very likely that one of your calipers are stuck.

Your brake system is hydraulic, meaning that when you press the brake pedal, fluid is pressured to all ends, forcing the caliper to squeeze the brake pads onto your rotors (or shoes onto your drums in older cars, and some newer trucks).

Old (and some defective newer) calipers stick, causing the pads constantly press against the rotor. If one side is sticking, it will wear the composite material on the pads down to the metal before the other side, causing a grinding condition only on that side. (likely what you're dealing with)

Sidenote: Typically, pads are replaced way before they wear down that far, because their semi-metallic composition combined with the nickel content of the rotor, and the subsequent friction from the contact causes the rotor to warp, resulting in a vibrating/thumping sound when the brake is applied.

Sidenote 2: Pads are usually replaced when warped rotors are replaced, because brake pads become glazed over after a period of usage, and that can transfer to a new rotor, making the braking system less effective. They're should also replaced when calipers are changed, since most effective semi-metallic pads are about $20 a pair, and since the system is pulled apart, it makes sense to do so.

Sidenote 3: Ceramic brake pads were introduced in the past few years that are supposed to avoid this warpage caused by the high heat that results from the pad/rotor friction. These pads can run about $80-100 per pair, but usually come with a lifetime warranty (good if you plan to keep your vehicle for 2-3 more years). I haven't used them, nor checked prices in quite a while, so my numbers may be a bit inaccurate for today.

Additionally, ask all of your friends and coworkers if their family has a mechanic they use. Under warranty or not, issues like plugging a tire hole, or routine brake replacement and exhaust pipe corrosion will cost you money.

A reliable mechanic who works out of their garage won't typically charge $60+/hour for labor, but by the job.

Those of us who do side work - computers, photography, personal training, auto repair - and dont' ahve to pay overhead costs like employees, shop rent and utilities, insurance, etc., don't mind charging for parts + $50 or 100, depending on the job. Even if it takes them 4 hours on a Saturday, $75 in their pocket makes their night or weekend of boozing free of charge for something they probably enjoy doing.

Some of these guys are more reliable than a garage, and even if they're just as reliable, you can save a lot of money, and most work evening/weekend hours.