Well it really depends on what you're looking to do. Do you want to twink yourself into some pimp gear, or just a kind of gradual upgrade strategy?
Personally you don't need a whole lot of stellar gear until you get alot higher as a mage. The pieces you will care about however are things like the book of spec monsters, etc etc. Other than that most of your gear will get replaced on 50's and 60's maps anyways, in addition to probably some nice mage pieces on the lower ones. So essentially my advice in short order is
1) Get a companion health item if you don't have one. Book of spec monsters is usually an affordable option here, and farmable with a mage in the 30's solo last I checked, so not all that far away.
2) Same w/ cp strength
3) Dmg inc is your friend, but usually expensive, unless you find a piece cheap thats pretty sweet its best to ignore it until your 50's where you can get a inc IV item free from farming maps.
4) Earring of black sapphire, oh how I love thee. Personally if I was going to save for some statgear for quite a while as a lowbie mage it would be these. They'll last you to 65 and beyond, never becoming an awful piece, and generally arent all that expensive. Though I havent been on in quite a while prices were around 350 for them. I think I saw them up to 500 though, but thats still not bad, especially when you consider you'll never have to pay anything..ever..to upgrade that slot.
5) Your starfalls kicketh much ass. As a mage you really do need these at lower levels. The staff could be soloed when I did it around 34-35. The ice is a bit harder because of the pain in the ass everchill orcs, ask someone big for help is my advice on that particular part. Then there's 2 slots that are reasonably good for quite a while taken care of.
6) rings...rings are a bit harder to find very quality ones on the market. you might want to go with some of the gold or if you can afford it plat intcaster rings. I would only really invest in one of them however, then start with the newport ring quests, as the final one of those will be on your toon's hand for a long long time unless you get lucky or have oodles of $$$$ to spend thus making the investment in 2 of them kind of pointless unless you can get the 2nd for say under 10pp.
7) Robeage..where art thou?? Take a group to miela grindy grind grind. Work your way up to watermage and once you can take him, farm him hard. Eventually you'll get a pretty decent robe that will last you quite a while. General price of it last time I checked was anywhere from 100-300pp w/an average price of 150.
8) A piece you may also want to keep an eye on is the royal crown from kaladim a. If you can find it cheap (around 100pp last I checked) you may want to snatch it up. If not take a friend or a few over to kala in the mid 30's to early 40's and farm it like no tomorrow, eventually one should turn up. The mana conservation is pretty helpful.
Warpstone may or may not have some decent pieces for you as well. It's been a while since I traveled through there much. MielA as I said earlier has stellar loot for mages in terms of bracelets robes and other things.
Other than that the only advice I can offer is to farm out tmaps as much as you can. Best way I've found is get a solid group of friends together w/the right makeup and decent gear, and get a whooooole bunch of maps. Then do em all at once. Make like a day of it. Not only will it be pretty good xp, but the loot is usually stellar. Unfortunately I don't know of any 20-40 pieces to reccomend as I was in the 50's when maps changed, and the only piece I have on an alt summons food, something ultimately useless to a mage. 50's maps pieces you will probably want
1) Shard of the ancient seers (Dmg Inc IV)
2) Barak's Moth eaten Mantle (cph IV)
3) Barak's magnificent Regalia (iirc that came from these)
4) Ring of the stout (clicky illusion dwarf and dmg reduction, handy for not having to load a shrink for your pet, also handy w/earthpet if you want him tanking in a group, dwarfing then shrinking seems to make him stay closer to the mob than he normally does. Should also be the only piece hard to get, as pretty much everyone will want it b/c of the illusion, and its really a tank item so let them have priority)
Mostly though don't concentrate on upgrading yourself too much now. Buy one or 2 good pieces and go grind. Most of your things will be coming from groups which ultimately saves you time.
