Generally you buy your dress, however sometimes the bride will buy it depending on her budget. You should talk to your friend and let her know you really want to be a part of her day but that you are working with a limited budget. Depending on how your friend is she may want your help in picking out dresses, this would be a great advantage to you because you could suggest dresses that fall within your price range.
I think you shouldn’t ask her to pick a different dress, but rather ask for her to go halters with you…. let her know that you’re kind of strapped for cash and that the plane ticket was expensive… I am sure she will understand… and hey you never know maybe she will end up buying them…. my parents and my fiancs parents went halters and bought my bridesmaid dresses so they only had to worry about their shoes…..
As a last resort, mention your money troubles to her. If she isn’t a total bride–and you handle it tactfully, of course–she may offer to help pay, especially if you offer to pay back over time. Typically, the bride does not pay for the dress unless she is well off herself. Check out some of the dresses at Target (they have a new line of high quality party dresses). Most sell for $50 or less.
If money is that tight, you can discuss with her if she is able to “go palsies” with you, or if she can select a less expensive dress, or if you can do a payment plan with her or something… Many brides these days just name a color and the bridesmaids all go get their own gown in that specified color.
You have to pay for your dress and you might not want to ask her to change the dress because it could cause some hard feelings. (She has a lot of decisions to make and although your complaint is legit, it is unfair to ask a bride to change the dress because one bridesmaid is unhappy with the style, color, price etc.) If you know the style of the dress you might want to look online to see if you can buy that dress in your size ff eBay or something. If you can’t and you do need to buy it, you can always sell it afterwards so you can at least get some of your money back.