Resiter button and payment

I would like to know if there is a plug in out there that is a event registration button that will allow them both the register and to pay.

Here is what I am trying to do. I want to add several workshops to my sight. Some will be free, othere there will be a charge. It would be nice to have a drop down box with events/dates & prices listed to register for and then a button to pay of there is a price attached.

I know I might need two plug ins, one for events with charges and one for events that are free. I am a novice, so I need something that is not complicated. Any suggestions? Any websites to go take a look at to see if I like the looks of the plug in?