I have 1742 RP left that I got as a gift. I can buy two champs from this group. I'm level 30, but i'm not a good player, although I enjoy the game. I mostly play BOT games and I hope to be good enough soon to play normal on a regular basis without getting yelled at. I seem to do better with:
1- Non-hybrids, straight up AD or AP...Can't ever seem to build Trinity fast enough.
2- Support, Mage, Anti-carry or straight up tanks with super-tanky builds.
3.- My best champs are Nami, Karthus, Urgot, Fiddlesticks and Maokai. I'm OK with Fiora and GangPlank.
4.- I don't farm well, unless Champ is good farmer like Karthus.
5.- I tend to love anything I can build Sunfire Cape on...Though I like the look of the old sunfire, pre-season 3 patch. BattleCast Urgot with old sunfire flames looked so cool I never lost with it LOL

So there is a little of my experience and playstyle. Here are the Champs I am considering. I own 62 so there aren't that many left.

Yorick
Talon
Kha'Zix
Elise
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Vayne
Trundle
Kog'Maw
Jarvan
Caitlyn
Xin Zhao
Udyr
Twitch
Karma
Gragas
Corki
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Malphite
Jax
Janna

Keep in mind that if I buy something from top group (975), that leaves only enough for one from bottom (585) group. Or I can buy any two from the bottom two groups.

I'm leaning toward Udyr, Vayne.... Malphite and Karma seem intriguing. What would you choose and why?

Don't buy any from the 3150 and under tier with RP, because IP is very easy to get and 3150 is generally not a huge wait. Consider buying 6300 champs (although RP should be more aimed towards skins and maybe IP boosts, but it's your choice).

Kha'Zix is a really fun jungle, he can tear people apart 1v1. Vayne is an amazing hyper carry, although you do have to be careful because your early game is not that good. Kog is the same way, although I would not go Kog in normal games if you don't have a team that is aimed at protecting him during a teamfight (otherwise he gets blown up). Talon is a good mid champion, especially with the new black cleaver. These are the only ones I have actually played and have input on that I think would be worth the buy, since you can easily save up 3150 ip for the other champs anyways.

ok TY..good stuff Baugh.....Let's just pretend everyone that money is no object though ok? LOL