My 2000 cadillac de ville has a blown head gasket. my mechanic tried to use "bars" but the engine overheats before it can take effect. are there any other cheap fixes ? it would only need to last a year

There are no cheap fixes for a head gasket tear and using Bars was about the worst idea he could have come up with. That stuff is indiscriminate - it'll plug up anything that resembles a rupture. If your head gasket is torn between a cylinder and a cooling jacket, then fine, but if it's an oil/coolant tear the Bars will be mixing into the oiling system and potentially clogging up oil capillaries in the head. Short answer though is no - a head gasket failure means the head(s) must be removed, the gasket changed, and everything reassembled. The only thing you can do in the mean time is take off tge radiator cap if you must drive it, so that the pressure in the system doesn't build and keep the thermostat closed. Do that and watch the coolant level and you can get away with a short hop here or there. That's it though.