just installed latest version of TC and checked. it takes less than 6 iron to make 32 tracks(RC recipe), smelting those tracks will result in 12 iron ingots.
You could make an interesting factory that automated the duping process and was self-sufficient. A very slight skill kicker would be that you had to find rather than craft the starter batch of rails needed. Abandoned mineshafts aren't super rare, but its an interesting form of 'seed' hunting.