Depending on where you shop, they may 'include' the keying in the 'regular' price. And, if you can wait, and one of their cylinders will fit into your lock, it shouldn't cost any more, since they can order them alike. Changing the cylinder once you get them can be easy or hard, depending on the brand of handle.
Medco cylinders use angled bottom pins...when you insert the key, they not only move up and down, but have to rotate to allow the cylinder to turn. I asked our locksmith at work about them, and he said in several classes, they were the only ones (presented to them anyway) that they could not pick, nor use a wax impression to copy. If you look at the key, the cuts are not aligned straight across, they're offset, which means few places can cut a key (if allowed and they can get a blank). Depending on the security level (for copying keys) you request, if you don't have the credit card like card they give you with the new keys, no credible locksmith will make a new one for you. Given that they are hard to come by, that is more secure, but as mentioned, making the door itself and the jam resistant to physical attack is far more important. A wood frame and/or door needs a lot of work to prevent it from being forced, and no lock will prevent that from happening. it's only if they are trying to be discrete that it helps. A medco cylinder is really hard to pick.