They should still get the best they can afford and replace the whole kit and caboodle. A middle of the road unit is going to be more efficient than a ten year old unit. They will also have the added benefit when selling to advertise new or newer HVAC and maybe extend a warranty. Good selling tool.

OK, the first guy that they called kept sounding less and less like it was a bad deal. It turns out that I had gotten bad info. The AC guy told the son-in-law, son-in-law told daughter, and daughter told me, so in the retelling, things had gotten jumbled. The $5600 estimate was a worst case scenario of indoor unit, outdoor unit, ducting, etc... using American Standard gear instead of Goodman. Not that I think that they needed all of that, but that wasn't really the guy's estimate. Today, they were still waiting for an estimate today, and the estimate was supposed to be for a 4ton goodman unit. They still haven't received that estimate so they called another company. Earlier today, the coordinator took their info, the tech called back 30 mins later, and they've already got an estimate. THe tech lives in their neighborhood. He told them that they should just get the leak(s) fixed. It's going to be $1200 to fix, evac and recharge, and he's going to do it Monday while they are at work.

The one guy did eventually come back and tell them that they had a 4 ton indoor unit an a 5 ton outdoor, so they were going to downsize. I'd never heard that the indoor units were measured in tons. 5 tons actually sounds a bit big for their house, but they aren't looking to replace anything, and it's been working, so it's going to stay.

Usually indoor coils don't go bad. Should be able to reuse it with new outdoor condensing unit. Rule of thumb: 800 s.f./ton of cooling. Well insulated home, about 3-31/2 tons. If indoor coil is larger than condensing unit, will have more dehumidifaction capacity. No need to change if within a ton rating. Usually installers match indoor coil/condensing unit to be same value. Slab or a coil on furnace? Cost of condensing unit about $1200-1500 per ton, based on seer. Higher seer, more efficiency, more cost. Difference in seer is based on condenser coil size. Larger coil=higher seer, more $$$. Goodman is at bottom end of hvac equipment. Carrier, Trane, York, Heil are high end.

1200 to fix a leak still seems hi.
I have not priced r22 since it went up.

a lot of the time they will go one size higher on the indoor unit. probably not good to go bigger on the outside but I don't know for sure. you might get away with it better with a TXV valve.
both are sized by tonnage.
look at the model number for each. divide the first 2 numbers by 12 and that is the tonnage.
EX: 24%&%& is a 2 ton unit
you may be able to get the year from the serial number.