Probably a Swordsman is still one of the better ones as a beginner (waaay back it was what I started RO with and I still think its a decent starter). I also like classes like Archer and Mage though because they can kill things from afar without getting hit to save on potions. Though Mage is really the cheapest, with Firewall you need never get hit unless (like me) you misplace it or don't cast it quick enough

Archers have the cost of their arrows to consider. Acolyte, well a Support Acolyte can be slow but as a Battle Acolyte (going to Monk or Battle Priest) I feel its pretty decent because you get a lot of buff skills and Heal etc. so it can be cheap as well. Battle Merchant ain't bad and you'll need to at least make 1 Merchant on your account for reducing cost of NPC items, increasing sale of items to NPCs and also for Vending to sell items you find to other players. Thief ain't bad because you get a lot of dodging capabilities too to save on potions and you get Steal to find extra items.
With the new Edens gear/quests most classes can get a good start so go for the one you think you'd find the most fun
http://irowiki.org/wiki/Eden_Group