In Malaysia, cheap accommodation and the community of expats + digital nomads don't go together. Inexpensive, however, is relative, and expats from more developed and stronger currency countries will find reasonably comfortable accommodation anywhere in Malaysia. A decent condo/apartment will start from MYR 2000 a month in Kuala Lumpur, which is only about USD 475 at current rates. A decent apartment for sale would start from MYR 600,000 or about USD 142,000.

The best place to search for a confluence of all your requirements is in Kuala Lumpur, or KL, as locals call it. There aren't any exclusive expat communities - at least not residentially - though Mont Kiara and Bangsar in KL have the heaviest expat population and will have a varied mix of nationalities, so your best bet at a community will be there.

4G/LTE bandwidth is not significant but is good enough in most cases, and coverage is extensive. Almost every decent cafe offers free wifi (Starbucks is all over town), and home internet connections go up to 100mbps for MYR 263 or USD 62 a month. Digital nomads are, in fact, all over the place, but official co-working spaces are not yet in fashion here.

Penang would be the alternative for digital nomads, but the expat population is far less concentrated there.