Hello, my name is Rusty. What will you be using the computer for? Give me a good scenario so I can narrow down your needs.
No, you only get charged once at the end, there are no hidden costs. I just want to give you the best answer possible, so, what are you looking to use the GR55 with?
Ok, you don't need a computer with the GK3 and GR55. The GK3 is a midi pickup, and the GR55 is your controller. It's plug and play as is. If you wanted to use a computer with it, you could do complex midi recordings, or even use a midi expander module to get more sounds out of it, but you don't need anything other than the GK3, the GR55 and an amplifier.