LOL, looks like you got alot of corn belt answers to a high plains question!

A Versatile with an atomjet kit might be about the cheapest option as far as something to pull an air seeder around. Actually, there are quite a few options (under $50K) for a 4X4 capable of handling an air seeder. Hydraulics are usually the most limiting factor. 91-93 Series Case IH-Steiger, Versatile 9*82-84, Cat track units, even the 90s era John Queeres are alot better than their predecessors.

As far as air seeders, a Flexicoil 5000 is the cheapest option if you can make one work. 12 inch spacing is ideal if no-tilling. Case IH SDX drills might be the best value as far as a decent disk drill.   John Deere drills are great, but as someone says, they are worn out or alot of $.  Case IH 500 drills are also good, but would be a similar situation.  I wouldnt bother with any kind of box drill, as John Deere is the only really good no-till unit, and it is usually highly overpriced.  Also, seeding is slow.

Anymore, pulltype sprayers are getting pretty cheap due to decreased popularity.  You could get one and find a decent tractor to pull it and handle other duties around the place.  On the other hand, dont overlook used sp sprayers.  It looks like Rogators are the best value, but it would be good to do some research about any particular model.

Im partial to Case IH Axials.  Good value, especially if you find a nice older model.  At least one semi and some support equipment for harvest would also be needed.

Not a complete list, but these are the major items.  Your exact needs probably depend on location and farming practices.