Note that while DMG p.54 says tho "subtract the value of a spellbook and material components from the average treasure value before you start rolling up treasure", the sample 5th-level NPC Wizard on page 125 has the following loadout:

Spellbook:
0—daze, detect magic, detect poison, flare, ghost sound, ray of frost, read magic;
1st—color spray, identify, mage armor, magic missile, magic weapon;
2nd—blur, bear’s endurance, glitterdust, knock, Melf’s acid arrow, resist energy;
3rd—dispel magic, fireball, haste, magic circle against good.

Possessions: Bracers of armor +1, rapier, masterwork hand crossbow, 10 bolts, cloak of resistance +1, potion of blur, potion of cure moderate wounds, potion of cure serious wounds, potion of haste, scroll of confusion, 2 scrolls of fireball, scroll of web, dagger.
The budget, for reference, is 4,300 gp for a 5th-level NPC.
Spoiler: maffs
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0th level spells: 7 pages = 700 gp
Other spells: 5 + 6x2 + 4x3 = 29 pages = 2,900 gp
Possession: 1,000 + 20 + 400 + 1000 + 2 = 2,422 gp
Consumables: 1 + 300 + 300 + 750 + 700 + 2x375 + 150 = 2,951

Grand total: 8,973 gp, or over budget by 4,673 gp.
(Even what PCs can sell it for, 4,486 gp, is over budget. For it to be below budget, the wizard would not only have to not have their spellbook with them, but they'd have to use half their consumable magic items in the battle.)


When it comes to actually funding these wizards, however, keep in mind PHB p.179:
Note that a wizard does not have to pay these costs in time or gold for the spells she gains for free at each new level. She simply adds these to her spellbook as part of her ongoing research.
Outfitting a wizard does not cost notably more than outfitting a fighter.

However, Goods & Services definitely implies that hiring one is more costly - a fifth-level Warrior will work for 15 silver pieces/day while a fifth-level Wizard will take one hundred times that per fireball. While a Fighter will probably take more money than 1.5gp/day, I'm not sure that it'd be the 500+ gp/day you'd expect from a Wizard in active duty.