30 mns commute takes in a large part of HK Island, Kowloon and the NT. You should play around with the Journey Planner on the MTR (commuter rail) website:
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and you'll find
Central - Tseun Wan on the Red line
Central - Kowloon Bay on the Red/Green Lines
Central - Chai Wan on the Blue Line
Central - Sha Tin on the Red/Green/East Rail line
Central - Hang Hau on the Blue/Purple line
are all within your time criteria, and all have affordable housing in your budget as do many of the areas along each way.