(S) How much would it be to fit this item

On my MK1 1.1 Punto

http://cgi.ebay.co.uk/TWIN-4-INCH-DT...QQcmdZViewItem

And what items would I need? I need a new exhaust because my exhaust seems to be having problems.

Compared with something like this?

http://cgi.ebay.co.uk/Fiat-Punto-mk1...QQcmdZViewItem

Will the performance of both be different i.e noise, tone

As long as the inlet pipe is the same size (otherwise you will need an adapter) then you would just need to cut off the other box and get some kind of bracket welded to the new one.

Only thing with Mk1 Puntos is it is quite a narrow gap where the backbox is, so it might not fit. I had this trouble when i wanted a universal sports backbox

So Run if you can, casn you find me a universal backbox that will fit my punto, imrpvoe noise and is cheap.

your best be is to go to someone like -

http://www.powerflowexhausts.net/

because the cost of getting brackets welded on and fitting will work out a simular cost anyway.
Cost of backbox fitted is about 130 quid from them, depending on type

or buy a used one from ebay

or get a sports one made for the Punto