I'll "second"or "third" the opinion that you NEED to have a qualified electrician give you an estimate on what is required for your hot tub installation. They will know the cost of increasing your service (dealing with the power company), and/or getting your existing wiring up to local code. Then you "could" do your own work as long as you get it inspected after.
I've never been a big fan of hot tubs... Yes they are nice to lay back in and relax, but the electrical bill and maintenance would cause me more consternation than what I would get out of it. They are best though if someone else pays the bills and does the maintenance.