Not sure I have a whole lot additional to add except to agree with what everyone else is saying.
A decent suspension lift, with nice riding 11 leaf rear springs is going to cost 700-800 or so. All vendors are going to be similarly priced for similar components.
How much does a paint job cost? How nice do you want it. You can literally spend as little ($200) or as much ($20,000) on a paint job. A nice daily driver paint job could easily be $5000 if you have the shop do the necessary blocking, sanding, body filler, etc.
Rusty floor pans, rockers, etc do take a lot more time than you'd think to replace UNLESS you are very experienced and have all the appropriate tools at your disposal. Or, if you pay a shop to do it, you're gonna pay their hourly rate.
Tires - depends on what kind of tires you want. If you just want some mudders, go to a nearby Farm and Rach store or rural Co-op. But, it sounds like you're wanting nice tires (Nittos or something). Up to you - the places mentioned have the best deals (Tire Rack, Discount Tire).
In GENERAL, you're not going to be able to BUILD one for cheaper than you can BUY ONE, if they were equal. UNLESSSS, you don't put any dollars toward your time and effort. Most people building them are doing it because:
a) they don't have the cash to lay out all at once
b) the joy is sometimes in the journey
c) they want to have complete control over the build and make the decisions, not buy someone elses.
How important are those things to you? You can buy a pretty slick ride for $12-15K and you might be a lot closer time and money wise than buying one for $3K and trying to get it there.
All your questions are really a matter of personal preference. I can tell you that the Bronco Vendors (Wild Horses, Jeffs Bronco Graveyard, Toms Bronco Parts, BC Broncos, etc.) are all great to talk to and will offer you advice. I'd call them.