Obviously this option isn't for everybody here, but preschools run out of churches tend to be screaming deals. DD's charges $130 per month for 3 days/week. We're not even part of that school's faith affiliation, but it's ecumenical and works for Christians of most denominations.
It's a shame that Montessori is now accessible only to the top-tier income levels (at least around here!) On the other hand, while education is extremely important to me, I see her preschool experience as being mostly for socialization and emotional readiness for Kindergarten.