Sound proofing a window

Now that i have moved off University Ave, the noise in to the master bedroom is pretty loud. Not that its so bad that I can't sleep through it, but on the weekends it might be nice to sleep in.

Apparently Home Depot has some as well. Given that I need a 3' x 4' area, it could get into $300+ to buy. 🙁 That is for material, curtains would be more expensive.

SoundProofing.org
http://www.soundproofing.org/sales/prices.html

Clear Vinyl Curtains and Opaque
http://www.soundproofing.org/infopages/curtains.htm

Sound Absorption Foam
http://www.markertek.com/MTStore/list.cfm?Idx=Sound+Absorption+Foam

Acoustical Foam
http://www.markertek.com/MTStore/list.cfm?Idx=Acoustic+Foam