For those of you with an Injen intake, how often should the filter be changed? And how much is a replacement filter?

i think you can just take it off, clean it and re-use it.

So, when would you need to clean/replace the filter?

So, when would you need to clean/replace the filter?
when it looks dirty

EVERY 30kmiles..

or when it looks dirty.

buy the k&n recharger kit.. it's worth the money..

don't over-oil the filter.. let it drip before putting back on, or you'll dirty up your MAF sensor and your idle will drop.

depending the driving conditions, check the filter everytime you do an oil change.