How much should I bring to Rodeo Drive?

In late July, I am taking my first trip to California (EEEEEEEEEEEK!). I'm super excited and I just read this book called the Hollywood Hills and it talked about this street called Rodeo Drive (Roh-day-oh NOT Roh-dee-oh). Anyway it's lined with designer shops liked Chanel and Burberry and Gucci. My question is, how much is a good amount if I just want to get one thing? I don't want to go all out...just something nice. I've saved up exactley $290 and I'm sure my dad will give me at least another $50. How much more do I need or do you think that's a good amount? I don't want to be like Julia Roberts in Pretty Woman when she gets kicked out! Any personal experience or comments would be fabulous:)