As Crodrules said, getting your own equipment activated is not a problem, although it might take a couple of calls to hit a CSR that doesn't press for a contract. One caveat when buying receivers though, make sure you're buying from a reputable seller that will back up the sale if there's any problems. Buying used on eBay in particular can be an issue if the seller is pushing equipment that has not been cleared by Dish because of an outstanding balance on an account. The receiver ID numbers can be verified by Dish before purchasing, and if a seller won't provide them, look elsewhere. New in the box units are not typically a problem though.
One reliable online retailer is
Solid Signal, but there are others as well