1999 Ford Explorer Ford Explorer engine cooling leak from u

(I know nothing about cars)
I have a coolant leak in my 99 ford explorer on the underside of the engine where the lower head gasket is. I bought the SUV from a friend of the family for $300 bucks. It ran hot on the previous owner, as soon as he seen it running hot he added more water and took it straight to the mechanic. It�s leaking from the gasket I think. I have used 2 bottles of blue devil trying to stop the leek (only slowed it down the leak stops when the engine warms up). I have been told that since you have to open up the engine I should change the timing chains, gaskets, and get new head boltsâ� ¦. I have talked to several people about getting this fixed and I�m getting a lot of different prices. I�m hoping for some help on prices ranges to get the repair work done, also on parts and prices of the parts. Thank you so much for your help. AJ Knight