Speaking theoretically, if you could do this, would there be a better way to make cash while gaining XP at the same time, other than solo Hill Giants from level 34 until they turn light blue around level 48 or 49? Are they the best cash/xp ratio in the game? Would this route give you the most possible cash? I know you cant really do it, I am just hypothosizing.

This sounds like a Quantity vs. Quality question. Yea, HGs are good cash. But once you reach that point where they turn light blue.... all you're really doing is farming them for plat. And for some, cash farming becomes very tedious, very fast.

Maybe try camping a few items for resale instead? There are quite a few posts here on ways to make cash in the Bazaar by selling items you farm, or doing the buy low-sell high game.

Once they hit blue move to bigger giants. I know the Ice Giants were good plat/exp in the upper 40's and SoV giants after that.

Dont overlook things you forage - if you can hunt in a zone where dye ingredients are foraged (100plat/per on 7th), or tufts of dire wolf fur (50-75 plat/per) for example you can make out like a bandit.

After you hit 49 and get yer good quadding nuke, the best place is Cobalt Scar. Quad wyverns non-stop =) Even if you haven't worked on CoV faction, it's still doable (in fact when I hunted there I was KOS and used this to my advantage hehe.. I could pull 12 in seconds :) )
The gems sell for 50p each to vendors (roughly) but check the bazaar because some are used in quests like kael armor and sell for 100p each or more in bazaar. The hides typically go for anywhere between 50p and 300p depending on yer server/market, AND while you med, hop on down to the beach (not in wolf form... the othmirs will kill j00) and fish for cobolt cod. U can sell the cod for 50p+ each or if you have brewing skill, go ahead and make cod oil (combine with water flask) and sell for 100p+ each.
On Tholuxe I usually make about 3k an hour if CS isn't too ubercamped.
In the 40's the best place to farm money is one or both of the Grimling caves in Tenebrous Mountains (offa Grimling) Don't hunt mobs out in the open. You'll make great PP selling the runes they drop to NPCs, the acrylia and windstones to players via bazaar, and if you happen to see the Grimling Runner, kill him and get a Rallic Pack to keep or sell =)

Hope this helps!
Teeny

Giants aren't doable at lvl 30 are they? Is so, where and which ones?
WEDruid

How do I get CoV faction, and is 39 or 40 ok to start on Grimlings?

in the 30's the younger hill Giants (commons) and the Cyclopses (SK) should be doable but they are too rare to actually use for exp.

Hill Giants are level 34 to 37. I went there at 33 for groups and soloed exclusively on giants up to 36 at which point I moved on to quadding spectres.