What's your definition of inexpensive? All things considered, the suckling pig at Manor Restaurant in CWB is rather worth its price. HKD500+ for a half pig, feeds about 5-6 pax.
For individual portions served w rice, some of the roast joints also dish out competent pigs, like Joy Hing, Yat Lok etc. They should cost you about 40-60 HKD per portion.