Well the mrs old man has done gear box swaps on C4's & while he was under the Lane he noticed tranny fluid leaking from the bell housing, I have been quote $400 to get this done by a shop & he told me to ring around for a kit, so how much is a kit for the main seal?

I've never heard of any kind of main seal exceeding $15. Do it yourself man, thats alot of cash for such a cheap part.

its a 30 min job do get to the seal on the tranny , but are you sure its not a rear main seal i would understand $400 for that

So if its both front & rear seals I wouldnt be up for more then $50 for both gaskets & 5L of trany fluid?

If you can pull out the gearbox by yourself its a piece of piss,my rear main only cost roughly 10-15 bucks and oil is 30 for 4 litres.
While the box is out i would recommend that you replace the coreplug at the back of the motor behind the flexplate, you dont want to have to remove the box again if the coreplug leaks down the track.
I would also replace the front transmission seal, you will need more than 4 litres of oil if you do the trans seal, replace all the accessible seals while you can.