Aside from airasia are there any other budget carriers flying between the above locations?

Try Lufthansa - they tend to offer low prices between KL and BKK

Skyscanner brings up all the airlines (other than AA at present) from KUL/BKK

LUFTHANSA indeed is BY FAR the cheapest option.

their RETURN TICKET is usually cheaper than AirAsia's ONE WAY TICKET !!!

BKK - KUL - BKK is 4.500 THB at the moment, INCLUDING all those things you pay for extra at AirAsia, such as luggage (23 KG free allowance), free seat reservation during the booking process, a snack and drink (no full meal though), free daily papers and magazines (if u r capable of reading German, that is ^^), private entertainment screen at your seat, PLUS - unlike THAI AIRWAYS - you even get a minimum of 500 Miles on any Star Alliance FF-account. And the cabin crews are much more pleasant than their reputation used to be.

Highly recommended - I use them 2-3 times a year on BKK-KUL-BKK trips

book on lufthansa.com to get those fares

Negative:

They only fly 4 times a week and the flight leaves BKK in the afternoon, arriving at KL at around 6.30 pm, so not much left of that day. return flight to BKK from KUL is at 9.15 pm, arriving in BKK 10.15 pm, which I find convenient.

ROYAL JORDANIAN and EGYPT AIR do both fly BKK-KUL as well, but they are usually more expensive and much less pleasant (I speak from experience, tried them both) - and RJ does not give miles in the cheap booking classes, so you cannot feed your ONEWORLD account

Try Lufthansa - they tend to offer low prices between KL and BKK

Next week it's Total Price: ฿ 5560.00

Which sounds like a good deal on Lufthansa.