The easy route:I have a lensless camera co. 75mm (wide angle) 4x5 that I love and it ran me about $60. The tougher route: I built an ultra wide 4x5 using layers of black matt board rubber cemented together, black cloth tape and black felt that takes standard and polaroid backs. I will search for the plans and let you know if I can find them. If not I can take a couple of digital pix monday and will be happy to walk you through it.
The 4x5 negatives really print beautifully.
Good luck