Buy the Haydel's double reed type calls. Less than $20 and they sound real good. They are plastic and dont change pitch when wet. I bought my two boys each one last year and they already sound better than some of the stuff I hear in the refuge....
As mentioned above any call from Hadel's is easy to blow. Also try Butch Gardner's 20.00 call, or The Primos Wrench. For about 35.00 you can get a call made by Echo (polycarbonite) that is durable and easy to blow.
Go to the Carlson website and buy their calling video. What ever call you buy - the tape will make you a much better caller. If you like the method they instruct on the tape, you might consider buying a Carlson Volochoke. Less than $50 buck and a very good call. If you just want to toot on the flute, you probably won't call many ducks in, but Haydel Duck Command and Primos make double reeds that can make an unoffensive quack. With duck calling, it's not as much the sound of the call, but the cadance and type of sounds you make when the duck reacts that counts. Buy the tape - you won't regret it. Carlson's website: http://www.duckcallers.org/ccc2.html
I'm going to disagree slightly with him about what call to get. I haven't tried the others mentioned, but I can strongly endorse the Duck Commander. Get the wood one, I think it's the #200. Sounds like a duck and is easy to use. My 7-year-old daughter called in a nice mallard drake her first try. True story.
True a double reed call will not do as much as a single reed, but you're just starting. Its better to learn how to do single quacks and read the birds, than try to start out with ringing come-backs and double-clucks. Once you are more comfortable reading the birds and calling to them you should move on to a single reed. By that time you'll know more about what your needs and preferences are. That is the time to consider a top quality call.