There are two types you can go for.
A BDA style one like this
http://www.ebay.co.uk/itm/Bmc-cda-en...f2850eb&_uhb=1
Or something like this
http://www.ebay.co.uk/itm/PEUGEOT-10...4ab2094&_uhb=1
Personally i'd go for the second one as i think they look better and tbh spending a 60-100 quid on an air filter for a 1.4 saxo really isn't worth the bother. But obviously thats your decision.
But you could always just buy a decent filter that goes into your existing air box and just atler the air feed.
These are often for sale in the for sale section on here, but you will need 100 posts and been a member for 30 days before being able to access them. Or you could please the mods and pay a tenner for the privilege now ha