Can you help me with this wedding registry/gift etiquette?

Dear Jelly friends, I need your help: one of my really good friends is getting married this coming June and I am to be one of her bridesmaids. I’ve only ever been to one wedding in my life and I was only 6 years of age at the time and it was in a different country with a totally different culture from the US. Also, needless to say, I’ve never been a bridesmaid, so my knowledge of pre-wedding protocol and etiquette in the US (especially as it pertains to me as a bridesmaid) is almost non-existent. As such, I have a few questions for the collective:

1) What are my duties/what is expected of me as a bridesmaid?
2) In terms of gifting, as long as it’s on the wedding registry, does the price point really matter? (I just checked her online registry and most of the items that are left are way out of my budget, but I don’t want to skimp on her gift because she’s a great friend and she and her family have always been very kind to me).
3) Also, is it acceptable to deviate from the registry when buying the gift?
4) What other handy advice can you give to this inexperienced bridesmaid/wedding-goer?

*Please keep in mind that 1) the bride and I live in different states, over 1,000 miles away, and 2) I’m on a tight budget, and will be even more so on the weeks preceding and following the wedding because I’ll be accounting for travel costs, unpaid time off work (5 days), expenses while away, unplanned expenses, etc, all of which will surely add up quickly.

Thanks in advance!