Only one sash (normally the bottom panel) is movable in the single-hung version; both sashes are movable in the double-hung version. Double-hung windows are easier to clean.
Hung Sash Window, Box Sash Window
In general, double-hung windows are more expensive than single-hung windows. (Single-hung windows typically cost 10%-25% less). Aluminum single-hung sash windows are usually the most economical (approximately $310 per unit). Vinyl single-hung sash windows are usually more expensive than their aluminum counterparts ($830), and wood tends to be the priciest option ($1240).
Costs vary greatly by region (and even by zip code). To get free estimates from local contractors, please indicate yours.