[Foxplay]

On the cheap end just (a few thousand plat) just focus on cheap +wisdom maybe some mana items...

Cone of mystics / Book of obulus - i think are the cheapest most bang for you buck primary and secondary's I could be wrong though

Frozen orb i think is the cheapest yet highest return range item - 3wis / 3int +40mana

platnium or velium +wisdom rings crafted by a jewellery maker

Since mana regen is fixed (unless you are getting buffed by other ppl) all your really focusing on is increasing your mana pool - try where you can afford to get items that have +wisdom AND +mana , rather than classic items that are just +wisdom, this may cost you a few hundred plat more per item , but you will get ALOT more mileage out of them, some of the cheap caster items from velious are typically used by level 60s waiting for raid upgrades

Crystal spider eyes
Coldain skin boots
Coldain skin gloves
Black sapphire electrum earrings x2
Platnium Tiara
Frozen Orb
Crystalline silk belt

While not currently in your budget these items will last you until 60 and beyond till you get raid upgrades

All this being said I will re-state the obvious, make sure you always have enough plat for your new spells, as a spell caster your primary upgrades are your spells make sure you have them / can afford them