Replacing gear box

[Ammy]

I have just recently purchased my first car, a second-hand 1996 Vauxhall Corsa. Whenever I put it into 2nd gear it usually 'pops' out after about 10 seconds. This is followed by a noise that is similar to metal being dragged on the ground. At the moment I have to whip it into 3rd gear as soon as possible or keep my hand on the gearstick to prevent it from moving.
Obviously this is extremely worrying and I would like to sort it out asap. I am assuming that the whole gear-box would need to be replaced(?). Can anyone tell me approximately how much I would be looking at for parts and fitting? BTW I live in East London.
Just to show my ignorance, is it the kind of thing I can go to somewhere like Kiwk Fit to sort out for me?

[homer75]

Scrapyard box maybe about �30 and find a mechanic to fit for you possibly another �50. Stay away from places like KwikFit - they will take you to the cleaners.

[alvin100]

I agree, definitely avoid the fast fit places.

Jumping out of gear is often a symptom of worn baulk rings caused by wear, Your car is a 96 so has probably done a fair few miles.
Your car will have an F10/F13/F16 box depending on the engine size, If you clean the gearbox casing you will see the type on it in letters about 3cm high These are commomly available from a scrappy or a gearbox specialist
Its probably a days work to change so expect to pay a days labour for the work.