2007 American Buffalo $50. How many versions of it out there? VERY confused !!!?

You go to U.S. Mint web site and it's all very simple. ONE American Buffalo Gold Proof Coin and ONE price of it --- $825.95

On Ebay there are 2 kinds of it:

1. 2007 American Buffalo $50 NGC PF70 Ultra Cameo . Cost $925.00

2. 2007 American Buffalo $50 NGC Gold MS70 Early Releases.
Cost $761.29

There are 2 different kinds of gold ? What is the difference between PF70 Ultra Cameo and Early Releases ??? Why is the first is more expensive?

I bought this 2007 American Buffalo $50 yesterday but the buyer did not specify is it Cameo or Early Releases. It was just stated - "2007 US MINT 1 OUNCE 24K SOLID GOLD $50 BUFFALO COIN" The total price is $802.67.

I didn't pay yet. Should I cancel the transaction ?

The last question - is it a good idea to invest in these 24K coins? Will the prices always go up for a long run? Any good books, resources where I can find some info about buying gold, esp. about coins?

I'm sorry if my questions look confused. Thank You.

Wow..You're covering a lot of territory here. I will try to answer at least part of this.
Your coin #1 above is PF70 or Proof 70. That is a proof coin and the highest grade possible.
Your coin #2 above is MS70 or Mint State 70. That is an uncirculated 'business strike' coin, and once again, 70 is the highest grade possible. The gold content is identical, but the appearance of the coin is quite different. The proof coins have mirror-like fields and frosted raised surfaces, which make them more attractive coins.
I personally think the 'Early Release' designation is something of a scam. There is no difference other than the early release coins were among the first struck.
As you describe your purchase, I can't tell if it is proof or uncirculated, or if it grades MS70/PF70 or lower (or if it has been graded / slabbed at all). Coins with the 70 grade are generally somewhat more expensive. Even an MS69 coin would be $50 less.
Overall, Gold coins such as these will do OK over the long run. I can think of many worse things to invest in.

Added later: I suppose I should say something about grading services, also. NGC is an independent third party grading service, not affiliated with the US Mint. PCGS and ANACS are the other two large grading services. There are many others, but they should be avoided completely. What they do is grade coins on a scale from 1 to 70, where 70 is the so-called perfect coin. They put the graded coins in a sealed plastic holder usually referred to as a slab, with the name of the grading service, the type and date of the coin, and the grade clearly indicated..
This is a very simplistic explanation, and once you get into it, you will have more questions. Amongst all the responders who clearly know nothing about coins or collecting, there are four or five very knowledgeable people here that regularly answer coin questions.