Advise needed: Maps

Can anyone explain how much high tier maps are worth and what kind of mods to roll on maps?

the highest tier maps can be pretty valuable. check on poe.trade

typically, the most wanted mods are more magic/rare monster and the ones affecting monster pack size

Unless you sell in bulk, maps start being worth selling at tier 8. Prices can be taken from poe.trade. Note that maps with easily traversable layout - i.e. no backtracking - like Canyon, Gorge or Plateau are worth a bit more than "complicated" maps like Orchard or Underground River.

Regarding mods: Some people just throw an orb (Alchemy or Transmutation) on a map and run it as soon as it won't kill them, while others reroll maps with Chaos or Alterations until they get high packsize/quantity. The higher the map, the more picky you should get with packsize/quantity. A nice guideline is to reroll tier 10+ maps until packsize * quantity is at least over 2,1 (so for example 80% quantity and 20% packsize = 1.8 * 1.2 = 2.16). However, if your build already can't do too many of the map mods (like Righetous Fire) then Alch + go might still be better. At tier 12+ it's probably worth it putting on a Zana mod as well (mainly Domination/Ambush/Beyond).