I feel so selfish - MOH?

One of my friends is getting married in September 2011 and has asked me to be her Maid Of Honour. I originally agreed to be part of her bridal party but now it seems like things won't work out. I have a two and a half year old daughter who will be three at that point and by then I'll also have a ten month old baby to look after and as bridesmaids/MOH we have to pay for our own transport, our own accessories and our own dresses. I can't afford to do that. She also told me as her MOH I have duties to stay until right at the end of the reception which I won't be able to do with two young children and I'll have to arrange and attend her hen night. She wants everyone to go pole dancing and then out on the town but that would cost £40 per person. I don't have that kind of money to throw away let alone to go pole dancing. I would be sat out watching due to back problems and not wanting to do it and I would still have to pay the £40.

In all honesty, I also don't want to be wrapped in a cadbury purple prom dress with netting and a white sash.

I feel so selfish but I just don't have the money to do it and I don't think I could provide all the duties she's looking for. Am I just being selfish and should I do it because she's my friend or should I pull out and give her chance to make other arrangements? I still want to attend her wedding but just not be a part of the bridal party.