Besides leaking a little oil (not much), the problem I noticed was oil in the water. Looking at the overflow tank, it looked like a chocolate milkshake. The car ran perfect. I have not heard of any leakage from the cylinders themselves, just oil leaking out of the engine and also into the water. I cannot seem how the "normal" 104 head gasket leak would give you the problems you are having.
As far as how big, rough figures are $1000 for each. Sometimes you get a break, others do not.