I was looking on my dashboard and seems that bitcoin is only available for the yearly payments.
Try switching to yearly and you should now see the option.
This is odd because my first monthly payment was effectively done with bitcoin (I wanted to try it out). This was some 10 months ago. Maybe it got changed in the meanwhile.
I just did the $4 plan right now, and it is asking for credit card, paypal. I do see the possibility of a gift code.
what am I missing here
also the captcha is not a possibility when I last tried over TOR. it was SMS only