Duno the area but eBay tend to be good for induction kits. What exact model saxo do you have as the engine changes at some point to an MPi.
Open filter means its not in a box, will be more powerful than the standard filter and a lot louder. A closed filter will pretty much only get cold air in as the box will block off the air around it, less of a noise though.
About £80 for mine from Race Dynamics in Andover, they deliver for an extra £8 though. K&N, + that's cheap.
Exhausts you'll find in a lot of places, just look for one you like the look of and ask the people selling what it's like. Remember though that you will need to pay on top of the pipe for fitting unless you can weld near a petrol tank. At the same time get the guy to weld out the middle box. Leave the catalytic converter there though as too mcuh hassle to put back on for the MOT.