It may be that they told you something you have not written here. It is
pretty difficult to snow somebody for two hundred dollars for just a
recharging. These are very common.So are the snow jobs,though.

If it is a pure 134a retrofit,you can buy a can of 134a and a hose/gauge at
Advance auto for about $25.You can reuse the hose ,next time and the
recharge will only cost $11,then.

Recharging is ez to do. The 134a hoses are quick release,so they wont scare
you to death attaching and removing them. 134a works at pressures  20%
higher than R12,so it will leakout that much faster.The hose will only
attach to the low side for charging.You cant make the mistake of attaching
to the high pressure side.

The Advance auto hose dosent use numbers on the gauge. Only three
colors,instead.Charge the system up till the needle is in the green
area,and you have done all you can do as far as a recharging goes.

Make sure you dont have a freeze 12 system,first.If your retro fit shop did
it right,they will put a sticker in the engine compartment that tells the
refrigerant used.

Good luck,Roger