My son just turned 6 and has been doing Kenpo Karate classes for 6 months or so. He recently added his second orange stripe to his yellow belt.
Pricing goes like this: $65/mo for classes - he goes to 1-2 each week - but there are 3 for which he qualifies. $15 for 30 min private lessons and the belt/stripe tests.
He hasn't wanted to go on Thursdays because they spar and he has to wear a cup...... My older daughters never wanted to miss sparring days. Saturday at 10 AM its all kids, all belt levels. This allows the kids to see where they are heading and it's nice to see them all helping each other. We were told that one belt a year was a reasonable pace if the student is motivated.
The school is staffed by a variety of students/instructors led by the owner, Scott Halsey. He is 5th degee black belt. He has been doing the school his whole adult life. Very accomplished, gentle and modest man. For the kids they make it fun, but expect them to learn what they are teaching. I haven't seen much higher level stuff, but the higher belts have incredible form.
Here is a recent article about Scott Halsey:
http://www.enjoymagazine.net/articles/article/id_cmsarticles/224
His amazing ability is teaching kids - and fostering those who chose to move along to higher levels. At some classes there are 30 kids - only he can manage them effectively, it's entertaining to watch. With a helper he has 25-30 kids, 4-7 years old cooperating with techniques etc. He knows all their names. Likely 250 or more students total.
He doesn't try to have this many kids - they just come because he offers a lot for the cost and makes it enjoyable for them.
Ask around where people are bring their kids. Hopefully there will be agreement about a good place.