I have to agree with Sabina41 on this again.
I'm going to urge you to pick up a dog from a shelter or rescue. If you're dead set on getting a puppy (which i think is silly) you can adopt one from a shelter/pound/rescue. If you get a mixed breed puppy you are much more likely to have a healthier puppy. Not always, but normally. It's called hybrid vigor. Each breed of dog comes from a certain core group of dogs, so all dogs of a certain breed are inbreed to a point. When you cross to breeds, you get different bloodlines in there and different genes, this helps to ward off certain genetic diseases and traits that are common in one breed but unheard of in another.
As Sabina41 said, adopting will be cheaper, adopting an adult will be much much cheaper. Call the vet clinics in your area and ask them how much office calls are, how much the first set of vaccines are, the second set and the third set. Then ask how much it costs to spay a dog and how much to neuter one. Then ask how much wormer costs, how much it costs to come in for an ear cleaning and how much the different medication for ear infections are, with a cocker, you're bound to have one sooner or later. Then add in the grooming cost.
This is what it would look like in my area.
Office call: $25 X 3= $75
puppies shots: 15X2= $30
Adult shot: $15
Rabies: $15
Neuter: $80
Spay: $100
HW prevention for 1 year (generic brand): $50
That's $265 for a male puppy and $285 for a female puppy. That also doesn't include an flea and/or tick prevention, grooming cost, the cost of the dog, the cost of food and supplies (collar, leash, treats, toys).
You can easily tack on another few hundred for the dog. So in a year you can look at spending WELL over $350 for a puppy
Let's look at adopting an adult dog
Office call: $25
Adult Shot: $15
Rabies: $15
HW Prevention for 1 year: $50
That's $105 dollars, not including the same things as above. I paid $20 for my rescue pup, but we got him at a discount because both my mom and i work for a vet. Also, with puppies from a shelter they're normally up to date on their vaccines so you wouldn't have that extra $30-$55 in there.
It's up to you, but if you're 14 and don't have a job, i'd go with the shelter pup.
Last questions. Why in the world do you want to use a cocker for agility?