Vinyl siding estimates

[tinker1121]

We need to replace our old siding on dormers and want the side of the house which is brick sided over. Front is stone so fine, back id t11 and want that gone over as well. House is a twin and approximatedly 8 squares of siding.
Problem is the varied estimates! From $2950 to $7,000. Why the difference and what is going rate per square and does that include taking off old and trimming out the windows. (Soffits and fascias are done so not including in these estimates.