If you are considering buying a house, remember my first axiom for used houses and cars and spouses. Know that if you think you want to change something before you even have it, what are you going to wish was different once you live with it every day? Know also that these things that you want to change can be much more expensive than your optimism lets you realize beforehand, and can be more difficult to change assuming you ever get to the point of doing so.
With that said, do this...
1. Have the home inspected by an ASHI approved home inspector. 2. Have 2-3 estimates for the siding you think you want installed done BEFORE you make an offer. 3. Get a real estate attorney to assist you with the purchase. They are the only person qualified to protect your interests and have no potential financial gain in the advice they give you in the transaction. (besides, the amount of paperwork you sign your name to will make you go blind, and no reasonable person could ever be expected to understand it all!) 4. Use the estimates from the siding contractors as a negotiation point in your offer.
Just getting a square foot price from your question won't work, because I have no idea what kind of siding you want, where you live, what the labor market is like there, etc... The price will be affected by how many corners there are, windows, doors, and other architectural features that drive up the labor rate. In other words, a square foot price is not very accurate when it comes to siding, because every house is unique.
Good luck in your process, and if you have specific legal questions, or house questions in the future, don't hesitate to post again. Our resident attorney is Regina in Il, and the rest of us help whereever we can.