5 years ago I paid 18K for a 1970 matching numbers 440U code, with 4-speed, dana 60 4.10 rear end, rallye gauges, rallye wheels, factory shaker hood and Super track pak. It was basically in pieces. It also needed a complete restoration and I ended up replacing the rear quarters, trunk floor pan and dutch-man panel. The rest of the car was very solid. The engine and trans had been rebuilt in 1983 but never installed. The dash cap had been redone along with all the seat covers and also not installed. It had been in storage since 1983. I know I paid top dollar for it, however it was matching numbers with a rebuilt engine, trans, and seat covers, etc.. I disassembled the engine just to make sure it had in fact been rebuilt and it had. I will change the cam, check the crank/rod bearing tolerances and have hardened seats put in the heads before I install it.
Is the 440 that comes with your aunts car a date correct motor? Also, you didn't say if the tri-power is included. If you can answer yes to both of these, then I'd say it would be worth something similar to what I paid, considering what it will be worth when restored. Not having the original engine will make a difference, but if it's date correct engine, while it will matter to purists, there are more that it will not make that much difference to as it's common to not have a matching numbers car now a days. If it's not a date correct 440 and you don't have the tri-power than I agree with MEK, about 10-13Kdepending on condition.