Air Asia is very affordable and the route network is extensive using KL as your hub.

Most of the SPG hotels in Malaysia are considered cheap and good value (if Platinum) compared to neighbouring countries. The Four Points is the cheapest and best value with its lounge (interestingly the Le Meridien in KK a short journey a way is one of the more expensive at ~RM600 a night and I'd say is poor value for Sabah). The Four Points in Penang is near enough to Georgetown and Penang has a lot to see as a tourist with great restaurants. You could easily spend time there. In KL, the Sheraton and Le Meridien are frequently available at ~RM300 and both have lounges. Le Meridien tends to get more expensive quicker but it does have the best lounge in the area. With both the Sheraton and Le Meridien you'd be able to be effectively on "full board". No beaches around KL though (Port Dickson is awful). The Four Points Puchong would be a bit cheaper but no lounge and, well, the location isn't exactly buzzing. In Sarawak, I had a good stay at the Marriott Miri for around RM300 a night. No lounge but nice resort and good beach nearby with great food.

Outside of Malaysia, you should look at the cheaper SPG hotels in Indonesia. If you want a resort then the Sheraton Senggigi on Lombok. Or there are some cheaper places in Bali now including a new (it's a refurb) Four Points in Seminyak that has good rates. The Sheraton Mustika Yogyakarta is also cheap, good quality with nice grounds and in a very interesting part of Indonesia with a lot to see. It has a lounge too that will suffice for an evening meal with booze.

In Thailand, I can really recommend Le Meridien Chiang Rai. It's cheap compared to other SPG hotels in Thailand but the quality is there. Suite upgrades and excellent breakfast. Sadly, it's been reported that they stopped the Platinum drinks in the bar each evening. It was a real bargain when they did that.