J.R.
I guess first I'd want to know what you are looking for in a preschool. What I was looking for was for a slightly structured environment, but freedom for kids to do art the way they want to (yes, SOME projects all the kids are going to make what looks pretty much identical, but I want to see a good opportunity for freedom of expression), pick some of their own toys, play with other kids. Lots of "big body movement" type activities along with sensory experiences. Not very much "academic" at this age.
I'm on the west end of Allentown, so I can't really reccommend a specific pre-school for you. I can say that at 4 years old my kids were (will be next year for the 4th) attending a preschool that is 3 half days per week, and that costs about $100 per month. It is at Bethany United Methodist Church in Allentown.
I will warn you...many preschools have already completed enrollment for the fall, so you may have difficulty finding a good one that has an opening. Bethany does enrollment in February.