5 speed to 6 speed?

Hi there, just having a think this morning. My only complaint about my 02 1.8 mx5 is the fuel consumption, she's rather thirsty. I suppose this is related to the 5 speed gearbox (probably the way I drive her too, LOL!)- I always feel that I could easily up another gear as I usually hit 5th very quickly.
I'm not all that knowledgable about the inner workings of my car, though I'm learning fast since I got 'Harriet'! Is it possible to replace the gearbox with a 6 speed, how much are you looking at, and what sort of improvements am I likely to see?
Thanks a mil
Sent from my HTC Desire using Tapatalk
I'm not all that knowledgable about the inner workings of my car, though I'm learning fast since I got 'Harriet'! Is it possible to replace the gearbox with a 6 speed, how much are you looking at, and what sort of improvements am I likely to see?
Thanks a mil

Sent from my HTC Desire using Tapatalk