Easy answer here. Wait till the expensive helmet is on closeout for 1/4 price. I got my bell star for $250. The little extra money vs a cheap helmet is very worth it when you turn your head at 100mph and get no shaking what so ever.
'06 F4i: racetech front springs+valves, ohlins rear shock, steel brake lines, 'mura slipon, 88K miles
'08 600RR- steel brake lines, shorty brake lever. Stripped track bike.
'15 1000RR- Flapper mod, 08-11 gauge swap, hotbodies fender eliminator