1

What kind of places are you interested in? Temples, theme parks, shopping, hiking, beaches, eating? Have you looked at www.discoverhongkong.com ?

What budget do you mean by cheap? Under US$50 means a hostel.

2

yes below 50usd..

3

Indulge in the serene atmosphere and traditional oriental architecture at Tai Sin Temple.
Marvel at the amazing bird’s eye view of Hong Kong from Victoria Peak.
Enjoy some leisurely time on the sun-drenched beaches at Repulse Bay.
Experience a crazy shopping at the multicultural-featured Stanley Market.

4

The Guardian has just updated their guide to HK.

http://www.guardian.co.uk/travel/series/hong-kong-city-guide

I would recommend

Star Ferry across Victoria Harbour (try to get there in time to see the free light show at 8pm every night - best from Tsim Sha Tsui side)
The Peak
Stanley (afternoon)
Horse racing at Happy Valley (most Wednesday nights. Just hop a tram to Happy Valley and it's HKD 10 to get in, HKD 20+ if you bet)
A ferry trip to one of the islands (Lamma or Cheung Chau)
Dim sum meal
Combine a visit to the Big Buddha with a look around the fishing village at Tai O (ferry from Central to Mui Wo and then a bus to Tai O and then a bus to the Buddha)
Markets in Kowloon - Temple Street / Ladies Market
Chi Lin Nunnery

N.B. Accommodation in HK is not cheap!