Given that your oldest has autism, and you have three so young, I think I would focus on getting close to your husband's work and working out a bike trailer solution that could carry his army crap if possible. Hauling "stuff" has many easy solutions--hauling 3 kids is trickier, especially given the special needs situation of your eldest. If he's not into that idea, even moving closer and driving will cut down daily gas costs and he may gradually embrace biking.
On your end, I would just try and plan as well as possible to go grocery shopping less often, combine it with trips to church/therapy if possible etc. Read on-line about batch cooking, strategies for shopping less etc.
If you do try out biking, I would make sure you have your eldest try out all the gear he will need (e.g., put on the helmet, get in the trailer or on the trail-a-cycle, put on all straps) and do serious test runs. As I'm sure you know, the sensory issues that are often associated with autism may cause extreme resistance to some required aspect of biking safely (alternatively he may LOVE the feel of his helmet or love the scenes rushing by while riding etc. and fight you when it's time to get off the bike etc.). I have a friend with a son who is on the autism spectrum and he loves riding in the trailer but SCREAMS whenever the bike stops, and fights getting out etc. You probably want to figure all that in when deciding what will work best for your family. Good luck!