Congratulations on your engagement and upcoming wedding! Just as someone else responded, times have changed and it is not up to the bride or bride's family to assume all the financial responsibility for the wedding. When I got married in 2002, my hubby (not his family) paid for the entire wedding including my dress, the rings, the accomodations, the church and services, reception, etc...and he definitely did not have a lot of money to do so. Ask your groom to be and his family to help. It might be easier to be specific about what you want them to pay for: cover the bill for flowers, cover dinner, cover the DJ...
Also, do what makes YOU happy. Trust me, there is no pleasing the in-laws...you will be much happier in the long run if you take care of what you want. The rest will fall into place. Besides, a wedding IS fancy- period. Don't let others push you into going over the top. It is very empowering once you take back control and do things the way you and fiance decide.
One last ditch effort and a more modern approach I have been hearing about... ask the places that provide your cake, gifts, music, flowers, reception, etc to DONATE to you in exchange for advertising. You write them up in the wedding/ service brochure, you have little mentions on the tables at the reception, you mention them on the microphone during the dancing... you get the idea.
Best of Luck and Warm Wishes! A.