Before you shift any turrets, stack boxes for you to get back up to the 2nd floor. After that, shoot all 3 turrets up the 2nd floor, then get the hell up there, set up one turret to one staircase, and then just use the last one as your gun.
Sort of a cheat without cheating. If you don't want to...
US$9.95 Includes Half-Life 2: Deathmatch, Half-Life 2: Lost Coast, Half-Life Deathmatch: Source, Half-Life 2: Episode One
Yeah, that's the cheapest package available.
As for the currency, http://www.xe.com/ucc/. Currency changer.