Its been years since I have been to Kerela - so would not know the cost of living at the moment. When I said Goa is cheap, I meant the food and booze. Booze in Goa is probably the cheapest in India. A bottle of Royal Stag whisky is about Rs.420 in most of the towns in the southern part of India - whereas in Goa the same costs about Rs.170 or less. Food, I think is cheap in the whole of India. Mumbai (formerly Bombay) is probably the costliest of all the places, almost the same as UK.
About 18 kilometers from Trivendrum, there is Kovalam beach and many new beaches have opened in the past that are getting popular. Details are available in
http://www.incredibleindia.org.
However, Goa is Goa at the end of the day...nothing can beat Goa in the whole of India, for its people, food, booze, beaches, laid back lifestyle and the general atmosphere...
Cheers!
Aj.