Electrolysis can be done anywhere on the body.
The expense of this will be determined upon how often you go, how long your sessions are, how effecient your practioner is, how many hairs he/she can remove in an hour, and lastly, the cost he/she charges per hour.
Shaving when you were 12 did not make more hair grow. Shaving does not have that effect on hair since it does not reach the dermal papilla. You were just destined to have a hairy back.
The good news is that electrolysis will permanently remove any hair you wish to be gone. If you have a large amount of back hair, however, you might find it advantageous to have a few laser treatments to reduce the amount of hair you have then catch all the hairs as they are reduced and as some might grow back in. Hope this helps.
Hopefully nobody scared you off from getting electrolysis done. I imagine you will be quite satisfied whenever you have gone through the entire process, we just hope to inform you of that process.
Whatever you chose, everyone here hopes it makes you happy and that we all contributed in some form or fashion. Keep us posted on whether or not you begin.