I run three groups a week for a total of about 9 hours playing time - some sessions are more intense than others. The pre game stuff is about 15 mins to half an hour but I have fairly detailed modules (each group is using a different one); each took a weekend to put together but will keep a group going for anywhere between 4 to 12 sessions. These have all the maps, hand outs, NPC's and items I need.
A $4.00 pdf (or so) in my experience will generally last a group about 1-2 months assuming that they play once per week for 3-4 hours and are reasonably pacey.
To convert one of these (depending on the intricacy of the maps - not a strength as Snikle knows) takes about 6 hours.
I should add that the biggest bugbear (pardon the pun) I have is players not showing up or those who show up for one session, get a free ruleset and vanish into the ether with what crudely equates to $20 or more of a ruleset ... YOU KNOW WHO YOU ARE (and my patience at this is wearing a little thin).