so I ended up going to Huay Xai anyway as I'd already paid for my room and bus back so made the best of it! I did do a border bounce at the same place over a year ago on the tourist visa before the new restrictions and yes you have to pay the $40 visa regardless if you actually step foot through into Laos or go straight back over the bus. Extra fees I think I paid 40bht for admin then 35bht for the bus ticket and my overnight bag, then I had to pay 20bht for some other admin fee too
you can extend to get a full year but I've been reading about it being super difficult recently so at the moment seems much easier to do a border run every 6 months