Yes, for the experimental builds you need to pay $5 minimum-- but doing so will allow you to download & play any experimental build released in the future, so you won't have to pay any more than that.
Probably when at the same time as the paid build, because it's been a while since either have been updated, non-paid is usually on a monthly basis, where as paid is meant to be weekly.
If you bought it on this account, scroll to the very top of this game's page. It should clearly say "You own this game" right on top there, and have a "Download" button right beneath it.
