Hi,
Can't help with the fitting but Lexus price is 184.00 Euros part # 90981-20005 based on RX300 2003 on, but try these guys
http://www.autobulbsdirect.co.uk/lexus-headlight-bulbs.html?gclid=CNLchIKl3aQCFdv92AodEzS5LA
or if you have the bulb type ebay
Just had a look on the exploded diagram ,headlight assy is secured with 3 bolts,one centre top,one on LHS (both fit vertically) and another which fits into the housing horizontally on the RHS (this is for the nearside headlamp)