I think there are a few issues circling here:
1.) Private schools (Montessori included) are going to reflect the prices the can charge in an area. By the bottom line business necessity, they will most likely be similar to other private schools in the area, and this will overall reflect the local economy and what people can afford and will pay. We live in a mid-sized western city where all the private elementary schools are between $6,000 and $6,500 a year. In other parts of the country, this would be outrageously cheap. So, how much a school costs will be a local question.
2.) Materials for doing at home- To me, the first question I want to ask is "How old is your DC?". For toddlers, the Montessori style and philosophies can be created and preserved without a lot of specific equiptment. There are a lot of 'practical life" things (washing tables, polishing, etc.), other things with beans, tonges, containers, hammer and nails, etc. The accessible and clear shelves, the emphasis on quality and beauty, the support of independence, the preservation of focus, the philosophies can certainly be adapted to the home environment of a toddler without fancy equiptment. At the preschool level, more of the specific tools come in- the beads, rods, pink tower, maps, etc. as well as a very detailed knowledge that the teacher/adult has regarding how Montessori views development and progression through works. That, I think, would get pretty pricey and definately raise the level of adult commitment and study. It really doesn't do the materials justice to just pick them up and "do them"- there are learning objectives, ideas behind the procedures, and variations intended for different skills and learning. In sum, I think that creating a "Montessori compatable" home environment for any aged child is certainly possible on a budget and parental interest, I think the "Whole Montessori Package" in a full-on homeschool framework from preschool forward is a significant undertaking in many ways.