DH and I never mentioned a word about presents or money or anything.... we don't believe in 'asking' for money or presents, but rather just the guests attendance was important to us. We're set up, have everything we need and we think it's a bit rude that people ask for money let alone a present.... whatever just happened to getting married and if you got a present or whatever it was a bonus!!

It does make it very difficult especially for those that can only afford $30 or so.... because I think many ppl would feel embarrassed at the $ amount they are giving whereas if it's a present they can hide how much they've spent iykwim.....
Good luck I hope it works out for you i dont really have any advice!! You could go against the grain and buy them a present of your choose, that way you can spend whatever you can afford and they don't need to know how much you spent. Just cos they ask for money doesnt mean you have to give money kwim??