I'm considering biking to school everyday, it's a fairly straight forward route, and the school is around 4 miles away. However, I do have to cross a park with its dirt roads on the way. So how much should a bike and helmet that suits my needs cost? Also, could you guys recommend any specific models? Should be reasonably cheap, and bear in mind I do have to lug a heavy backpack around. The sidewalk laws are also confusing me a bit, how are those in California? I tried Google, and the result says that I can ride on the sidewalk, but not in certain areas, how should I look out for those areas?