Define sensible as Bangkok and Thailand is stilk relatively cheap. We’ve used New Siam and New Siam 2 off Rambuttri several times, so cheap you can have non-aircon rooms if you want to save a few quid but has a pool and decent priced food.
Lots of stuff near but not on Koh San Rd (which is like benidorm or Blackpool in it’s tackiness), so Rambuttri a better shout unless you really want that backpacker experience.
Stayed at Chillax last year, a step up from New Siam and similar budget fare but the name made me wince 😉
And it’s not called Burma anymore 😉 We did a week on a live-aboard diving ‘Burmese’ islands last year, their move towards democracy means they are opening up to tourism much more now but still decades behind Thailand etc in terms of being developed/exploited/spoilt (not being a traveller snob as we love Thailand and seem to go back every 2 years).