Personally I don't want my tenants cleaning screens or windows that requires taking anything apart (they will likely succeed in breaking something!), or anything that might be considered dangerous (such as standing on a rickety ladder to clean a 2nd floor window). Hopefully you received a list of things to do for your move out. If not, check your lease. If there is nothing in the lease or there wasn't anything provided to you that indicated you must clean the windows and screens, then in my opinion you shouldn't have to pay to have that work done.
Other LL's in this forum may not agree with me, but I'm just giving you my honest opinion.