Don't use gox. You don't have to use those markets either. There are others or you could buy from the forums here, just use a trusted escrow and you should be set. You might be able to find a better deal here than on those platforms too.
Preev is a average of a handful of the major exchanges if you want to get your price from there:
http://preev.com/btc/usdAs of now I have no plans to invest in BTC, I prefer to mine since there's no risk (I certainly don't know enough about crytocurrencies in general to dare wagering money on it.)
But I just want to know how much I should expect to sell the BTC for at the current market. Do you not sell BTC directly to a market? Do you have to sell directly to other people (can you detect my level of cluelessness by now?

)
If you generally only sell BTC to other people, then is the average market worth what you sell for?
Do you already have mining gear? If not, you'll kinda be wagering money on it by investing in a mining rig. You can sell coins for whatever people will pay for them, but generally people use either preev or another exchange for the price.