You could encourage your husband to work with him on some fun things, and you can work with him on the weekends. There are free story groups in most libraries, and some book stores. You can also hook up with a play group that is available on your time.
During summer there are Vacation Bible Schools that go for a week each for very cheap or free. Summer day camp can also provide a little social structure for a while. You could also talk to people you know who would be willing to come over and work with him for a bit on some days.
Here's a nice long run on sentence for you. The main things he should know before Kindergarten are his ABC's, counting by 1's 2's 5's and 10's, adding small amounts, recognizing letters, blending sounds, rhyming, words with the same beginning or ending sound, continuing patterns, shapes, colors, sorting, cutting, coloring, gluing, stacking and building, days, months, years, seasons, dressing himself, tying, zipping, and snapping, holding a pencil or crayon correctly, parts of books, illustrator and author, going from left to right while reading, hearing books read, reading a bit, answering questions about what was read, guessing what might happen, using imagination, coming up with ideas, some easy sight words, his name, address, and phone number, manners, cleaning up, listening, focusing, speaking, lining up, taking turns, sharing and compromise, and following directions. Many of these things like counting and letter sounds, you can easily have him go over in the car or while you are fixing clothes, food or whatever. Many things you teach him in everyday life and should come naturally after a while. There is more covered now then there was several years ago, but as long as you work with him on normal toddler and prek stuff, he should be fine.
There are some good prek programs on TV on PBS, Noggin, etc. There are also some good computer programs for pre-k, and the internet has lots of sites like starfall and PBS kids, with educational games that are free.
If you really want him in a school setting before VPK most churches with prek tend to be less expensive then other prek's. You can also check to see if he would qualify for Head Start. Even if you don't get him into school this coming year, he will still be able to attend VPK the following year because Kindergarten has the same cut-off dates that VPK does.