How much time/money?
Modifying the hubs is the cheapest since it is free. However you still have weaker plastic hubs.
AVMs are good, inexpensive, huge improvement in functionality, but still weaker like factory hubs. You won't lose mpg since they can stay unlocked (although mileage loss should be minimal if detectable at all). Super easy/quick install. This is what I did on my 98 ranger, but would probably swap to live axles if I did it again.
Live axles require hub/bearings and axleshafts from a liveaxle truck (new or donor). 00.5+ rangers, 95+ explorers, 01-05 sport trac. Cost is higher (normally) and it involves a little more work. Really the only downside (in my opinion) is that you cannot unlock the hub if a CV joint breaks. CV failures are rare though unless you are running an RCD lift, or huge tires with lockers, etc. I ran 33s with 4.88s and a front locker and didn't break anything during that time.
2006 F150 FX4 Super Crew - Bilstien 5100s leveled 2", 35" KM2s, 4.56 gears, Detroit locker, Eaton E-Locker, Traction Bars, AEM intake, Xcal 2
2010 VW Golf TDI 6MT