Oh, no, Tuen Mun proper is still okay, I just assumed HKChigger meant more remote places around that area - quite frankly I didn't know you could get that much space for that price in Tuen Mun itself.
even the rent in shatin is pretty high, but you more than likely to get 350 sq ft for HK$4k, than 200 sq ft in sheung wan!
possibly cheaper places would include sham shui po, kwun tong, ma tau wai and even parts of hung hom
i have two cousins, each of them paying not more than $5k/month. one lives in Tin Hau (i think) and the other in Kowloon City. VERY small accomodations. the one on HK island has a studio. the one in Kowloon City has actual bedrooms (2 of them) but both are VERY small, as is the "living room"