To throw in a couple of options, "near" Bangkok (i.e. a 2-3 hour drive away), and the following will be cheap (ish, by Marriott standard) - but no kitchenette as far as I am aware. I suspect that a central Bangkok hotel may also be cheaper than any of these options, but they are more beach-resort places:
- Renaissance Pattaya Resort & Spa - Not actually in Pattaya, but a nice place with a beach, though you will live in the hotel so any "value" is likely to be eroded in spending.
- Courtyard by Marriott North Pattaya - In the middle of Pattaya, you could likely eat and live cheaply here most nights, but ultimately it is a Courtyard hotel. It is more cheap than good value I'd suggest
- Rayong Marriott Resort & Spa - Likely to be the cheapest resort around the Bangkok coastline. Reviews say it is a bit run-down (it's why I haven't stayed yet, I keep returning to the Renaissance Pattaya), but it will give you beach and relaxing for probably 20% less than any of the Pattaya hotels
- Hua Hin Marriott Resort & Spa - There are a couple of Marriott hotels in Hua Hin, again the same idea as the ones above, by a beach, about 3 hours from Bangkok, nice hotel, going to be cheaper than Phuket most of the time, busy at weekends with Bangkok residents and a reasonable hotel. Believe this one is cheaper than the Sheraton Hua Hin Resort & Spa
- Sheraton Hua Hin Pranburi Villas - Moving away from cheap, but if you want more of a "home", then these could be for you. I haven't stayed but there are mixed reviews on elite benefits since your chance of an upgrade is limited