You may be able to look around and find cheaper prices, but the only correct price is the one on the cruise line web site.
By the nature of programming for cruise booking engines they do not update in real time (usually just once a day), so even if you see a great price at any travel agent web site most likely it is an error and if you call you will be told the cruise line's price.
It is absolutely not allowed to discount by a travel agent, but some do get away with it by sending the customer a portion of their commission check when the cruise is over. No, I can't tell you which agents do this, but I have seen their ads here in this site (probably fed to us by Google ads).
But I agree with Pete - I would rather use an agent and get the same price as the cruise line, but get all the added service a good travel agent provides.
Getting to Oasis - we have neighbors book on it as well, and I saw their quote. Another thing you want to do is to check the price before you make final payment. If it has gone down you can request a price adjustment.