They're charging you that much for 4 weeks? I did 3 weeks in Aussiefor $2800 in 1999, and my entire 6-month trip to Aussie in 2002 (including a semester of school and travelling to 4 countries) was $6,000, and I wasn't too thrifty.
Aside from that cost, studying abroad was the single best experience in my life. I know a semester is different from 4 weeks, but being immersed in another culture really opens your eyes. Whatever you do, do NOT ruin your experience by being homesick. I've seen far too many people not get their full experience by spending all their time crying on the phone to people at home. I didn't see anyone I knew for 6 months, but I survived, and you can, too
I'd say go for it!