X2 gave a real good advice about the downpayment. That makes more sence if your parents really want to give you some thing.
If your in laws are saying no to it right now I highly doubt they are the kind of people who'll bug you later & as far as husbands are concerned. I have noticed even if they are illiterate they don't give a damn about this whole jahez issue. Its sometimes the mil who are greedy or whatever you wanna call it.
Also its not people in USA who are declining jahez. Its becoming a common practice in Pakistan too.