When you say lawn I'm thinking Gul Ahmed, Sana Safinaz and Al Karam type. Even their full embroidery ones may not be appropriate for Valima!! Guests will be more dressed up than you.
But, it's your shaadi so wear whatever you like!!!! :)if you really wanna wear something cheaper and lawn, why not get a cotton dress with silk Patis and good embroidery and a chiffon dupata? How much will that cost? Is Sharmila Farooqi wearing lawn? Looks like a chiffon semi formal type dress
are you having your walima at home? For a banquet hall event, I don't think lawn is appropriate at all. There is no requirement to wear something heavy and full of work. You can opt for a light, semi-formal dress instead. But you want to stand out from the crowd and look polished.
Thanks a lot everyone for your suggestions but I don't think I'm going to win this battle. The clothes have been bought for the engagement. Expensive. No control. It sucks.