2 modes between HK and Macau - Helicopter and high speed ferry.
Helicopter is (as you may have guessed) very expensive. It could be more expensive than your air fare on Tiger.
High speed ferry takes about an hour. Very frequent schedule and comfortable. Here's a link for more info
http://www.turbojet.com.hk/turbojet_sailing_rev.htm
Mind the point that you will incur other land travel costs if you travel via Macau. Also, being unfamiliar with the country, you might not be able to find the most economical mode. As with other countries, a foreigner might fall victim to dishonest people as well. This is not intended to flame Macau, but being in a foreign land, the risk is always there wherever you go.
Personally, I would take the reverse route - land in HK and make a short trip to Macau. Nonetheless, this is a matter of personal preference. No absolute right or wrong.
My 2 cents. Hope this helps.