would it be economical for me to take MTR or bus to Central then a cab to the Peak?

Yes, it will be economical if taking the bus or MTR to reach the Central. Then you can walk to the Tram Station at Garden Road. the whole tram ride takes about 8 mins, but you may have to line up for at least 20-30min to board the tram, unless you arrive there very early in the morning. Anyway, to save time, you can surely directly take a taxi to the peak.