If you had transferred 65k every month (for 12 months of your current visa period) without fail from UK to Thai bank account, you wouldn’t need 800k in the bank for your subsequent application.
You need $40 USD for visa on arrival. You can pay 1500 bht also. I downloaded the visa application form, printed and filled it in before I left Thailand. I escaped the queues for forms and pens and was through in 10 minutes.
The place is so cheap it’s unbelievable. Airport is right inside Vientiane so quick airport taxi to hotel, standard cost is 180,000 Lak, which is around £6.50.
I stayed at an expensive hotel as I was meeting up with friends who had already booked there. But you can use Agoda to find somewhere desirable. The first time I went I stayed down by the river. Try look for a place close-ish to The Tipsy Elephant Roof Top Bar. That’s where most bars restaurants are. Taxis to places from our hotel were no more than 50k - 70k Lak (£2 - £3) using an app called Loca, similar to BOLT, which you can also use there. Food and beer is dirt cheap, even in the nicer venues.
Most places accept Thai baht as payment so no real need to exchange money. You will get baht or Lak back in change.
NOTE: Vientiane is much quieter than anywhere in Thailand. Not much happening at all. So expect a very relaxing and quiet day or two. But if you fancy a beer with some live music I’d recommend Wind West bar. Cosy place with a good atmosphere. Because of the lack of choice, we also went to Hard Rock, not my usual go to, but it was ok.