I've been a bridesmaid a couple of times.
First one dress was paid for but I then paid for shoes, accessories, hair and makeup,hotel, etc.
Second time the bridge and groom paid for everything
Third time I paid for everything
Fourth time dress and shoes were paid by bride and groom
Fifth time I paid for everything (but the bride was very chill - just asked her bridesmaids to get a purple dress, no other demands) and we stayed in a Travelodge
Sixth time I paid for everything
Now my friends are mostly married - dd has been a flower girl once and we paid for her dress.
I think if you're struggling to afford the dress then maybe bow out gracefully - add in all the other costs associated with being a bridesmaid like hotel, makeup, hen party, 'planning lunches', etc etc.