You can pick up Arai's cheap from the states thru ebay - look for seller flyin brian all the lates lids and does deals for multiple lids although they dont come with the BSA kite mark as they are U.S which some tracks look for(espec bike ones cars dont bother to much as long as they are in good nick)
Arai's are dear but worth the money althought they dont fit everyones napper perfect.If you own one pop along to a mojor bike race and look for their support van they will do a free service/checks on it and will swap parts on it normally free.I own one Arai astro, 2 Shark RSF's and another matt black cheapo for trackdays.