Duck calls are like violins. Some can play them and some can not. It takes a good ear and practice to get the most out of your natural talent. Then you can refine it to suit your hunting situation. Do not make the mistake of falling in love with the "high volume hail" calling because they often sound like crap at fifty yards. Buy a good CD on calling and listen to it until you can understand "duck" like you do English.
In late season you will find ducks have been called to death and will respond to just the bare minimum amount of calling while large amounts of calling, even good calling, will repel them like gunfire. Look at it from the ducks viewpoint. They have heard the same bad calling for months, start to land in the decoys only to have a near death experience but some duck hunter who could not hit a barn door with a shovel. Talk about negative reinforcement.
First thing to determine is what type of hunting area will you be in. Heavy timber, blinds of the banks of a small stream or small river or a blind in open water. That in part will help you select the type of calls to buy. Expect to spend from 50-100 per call for a decent call. Acrylic calls should be in your mix but not all acrylic calls or all wood.
Always have at least one goose call on your rig. If I had a dollar for every time I heard a duck hunter say he forgot his goose call while he was duck hunting because he did not think he get a chance to call a lone goose into decoys I could by the entire bbs each a box of shells. Getting a single goose into range that way is a very rewarding event. It is your calling that they are responding to not the decoy layout because you did not have a single goose decoy out there. 100% you.
If you have a lathe you can turn your own calls. The internal parts are easy to buy, simple to rough tune and make a decent call for a few dollars. If you get into it really big you can buy a jig to cut and make your own parts so the entire call is custom hand make in your shop. Do a web search for call maker sites or drop me a PM.
Just be cause a calling contest winner can blow a call does not mean you can as well. Did that stars name on your bat as a kid make you into a major league hitter? Many of the custom calls are tuned for non hunting conditions. A call contest takes a different call than hunting does. You are preforming to a audience of call judges not ducks. Completely different audience. Take one of the contest call out into the marsh and it just in not setup correctly. It will sound good to your ear but you are not the judge in this case. That judge has feathers and has been hearing first class duck speak for his or her entire life.
Practice is the key. Money will not make you better past buying decent calls. If you are tone deaf you will never call worth a darn. But it you have a little talent, and work at it, ducks will come near. Then you had better have been practice your shooting as well. Bang, bang, bang is often the final duck call in the marsh.