Depends where you're flying from. Gatwick do charter flights, but you can also get there via Dubai to Trivandrum, so that brings you into range of Manchester and Birmingham flying with Emirates on a straight through ticket.
They were going for about £450 when the route started earlier this year.

Don't know what the hotel deals are like, but it gives you an idea of the independent flight costings.

Thanks Chriss
Have found a flight for £433 but not phoned yet so there may be some additives on top. Packages are about £650 ish so would need hotel to cost £60 p/w to make it viable
Netleyneil

I think you have answered your own question on price, package tours are cheaper by and large. The problem is finding a three week one. First Choice operate 2 weekly to Kerela, but you can go to Goa for three.