Just to elaborate on what Gary said, my first proper drum was outsourced and cost £150. That was with all the material provided and with free machining so if you were to pay for machining and didn't supply the material it would cost a lot more. By comparison, my most recent drum cost perhaps £10, but that was achievable mostly due to the goodwill of others supplying pieces, workshop time and machine work. So the cost of making a drum spinning element is really like the age-old question of how long is a piece of string?

As for ratios, again it depends on what motor you use, what your desired output speed is and so on but for reference, Drumroll II running on a Speed 900 motor at 19.2V has a ratio of 2.2: 1 (a 44-tooth pulley on the drum and 20-tooth pulley on the motor).
When I used a brushless motor for a while, it was a ratio of 5:1 as the brushless had a higher rpm and needed a bit more torque when starting up. So it's all just a case of tailoring it to suit your individual needs or preferences.

EDIT: Brushless motors certainly make spinners a more lethal proposition but they are not the be-all-and-end-all of spinning methods. Brushed motors are a perfectly suitable alternative; for the past three years at the UK FW champs, a spinner has finished 3rd, and all those spinners used Speed 900s as weapon motors so they can do the job. It's more difficult to get a brushless spinner setup running reliably; Dave Moulds (360) went through several motors, controllers and money to get his disc running well. In the end though, the more important factors are the properties of your spinner itself (such as mass distribution, moment of inertia and, to a degree, cutter bite)