Whats a good entry-mid wheelset for a salsa fargo?

We don't really do product recommendations per the frequently asked questions. Links to manufacturer or shop websites will frequently go stale, and furthermore bicycles and the bike industry are evolving quite rapidly - particularly gravel bikes and their gear.

That said, it's possible to discuss some generalities. The practice of having two separate wheelsets is not uncommon for multipurpose bikes like the Salsa Fargo, which Salsa describes as an off-road touring and bikepacking bike (although clearly, nothing stops you from using it primarily on road). If you use tubeless tires, then because those tires are more troublesome to mount and dismount, having two sets of wheels with different tires could save you effort. If you wanted a wheelset that was more performance road focused, e.g. aero rims with 28mm tires, then that could be another reason to maintain a separate wheelset. However, you have to buy the wheels, and a pair of rotors, and another cassette unless you want to swap cassettes back and forth. Some riders keep one 650B and one 700c wheelset, with the 650B set getting wider tires for even more technical off-road terrain.

Depending on what your gravel looks like, it's possible that some people might be able to use a wide slick tire, and that would tend to bias me away from maintaining two separate wheelsets - I'm thinking gravel that's mainly dry, because knobs are objectively needed in the mud, whereas I'm not sure that knobs help a lot on dry gravel. If you feel like you can actually cover your intended needs with one pair of tires, you might not want to get a second wheelset. If you're not running your tires tubeless, then it's easier to change tires back and forth - however, tubeless is generally recommended off-road.