What would be a decent amount of money to bring (for shopping) on a trip to Bangkok, Thailand?

I'm 13 and taking a family trip to Bangkok soon. I heard everything there is really cheap and because of that my mom said I would have to supply my own shopping / souvenir money. We are going there for maybe a week or so and I've been told multiple times to come with nothing but a large, empty luggage bag and some spending cash. But how much should I bring? I have about $150 right now... is that enough? What could it get me?