So personal attendant is essentially an unpaid slave for the day? She should be thanking you for doing it. (I've never heard of it, beyond I've heard rumors people who are Coordinators will be Day of Coordinators for their friends as a wedding gift.)
I agree to decline up front or tell people you'd love to be a bridesmaid, but you have budget constraints, and find out the expectations before accepting. Then, make them stick to it. (Not object over $15, but if they said the dress would be about $150, I'd feel 100% ok bringing it up if the bride suggested a $300 dress.)
As a guest: I would attend the wedding and give a gift. Attend local showers and give a gift. Attend a local engagement party (no gift - but it's not really the thing to hold these or expect gifts if you do, maybe a card) if I wanted to, but I would not feel obligated to attend an expensive event.
As a bridesmaid: I would expect a lot higher expenses - attire added to the others. I'd attend all local events and give gifts the same as above. It would depend on the bride whether I'd feel obligated to fly out for a non-local party (I'd hope not but some are unreasonable. Neither of my long-distance bridesmaids flew out for my shower, and my bachelorette was just dinner/drinks just before the wedding to make it easier for one of the two to come. I'd make more of an effort for a sister than anyone else.) If I couldn't attend an expensive bachelorette, I'd send on a bottle of bubbly. I did that for my SIL-to-be who planned a trip to Cabo.
Share hotels. Hunt for cheaper priced hotels. Ask the bride about a hotel block at a cheap place. Stay with friends when possible.
Deal hunt for wedding gifts, using all codes I can (hint: buy around major holidays). If you find cheaper elsewhere, buy and call registry place to get it checked off. Think handmade as well.
YOU (well the bridesmaids) plan the bachelorette, not the bride. So that's an easy way to rein in costs by not planning something elaborate. (These have really gotten out of hand.) Worst case, have the balls to say "I'm really sorry, but this event is out of my budget. I love you, hope you have a great time and I'll be there in spirit - I just can't attend in person.") You just need to make sure there aren't any crazy planners on the bridesmaid team, and talk them down if so.