I never took a formal ground school when I was learning to fly; I preferred the self study format with CBTs and/or interactive video courses (like King). But anyway, you need to look at what your course objectives are and what your likely target audience would prefer when it comes to scheduling issues. You stated that two options would be to 1) offer a weekend course (presumably approx. 16 hours of instruction), or 2) offer a four week course, 2 days per week, four hours per night (presumably 32 hours of instruction), so obviously one format can go way more in-depth than the other. You also said this course would be sport/private/IFR, so you're really talking about three separate courses, right? 16 hours, or the weekend format, is probably sufficient to prepare a student for a single written test. If you're trying to put together a course that would prepare a student for BOTH the private and the instrument writtens, you're probably looking at the 32-hour (or more) format. Or is the objective to go "beyond the written" and more in-depth into the individual topics by offering a 32-hour private course or instrument course over four weeks? Again, you have to look at your clientele. If you're dealing with professionals who have a day job, I doubt they're willing to hang around for more than four hours on a work night and would prefer a weekend course; if you're dealing with students who aren't doing anything other than learning how to fly, then you have a bit more flexability and could maybe even run a M-F class during normal "school hours".
I think I paid $189 for the King private course back in the day; would probably be willing to pay up to $250 for a quality groundschool with the option of free recurrent training. As for a course taught by airline pilots; that's a great marketing gimick, although I'd expect the instructor of a sport/private/instrument course to have general aviation credentials. Airline captains are great at instructing first officers who are already qualified pilots in that specific airline's way of doing things, but I know many airline pilots who don't know squat about VFR flying or how to take someone off the street from zero hours to a PPL. I haven't instructed in years, so I'm probably not the guy you want teaching a PPL groundschool since I'm not as "up to date" on that kind of flying as the CFIs who are actively instructing new students. If you can find an airline pilot who is still very active in the general aviation community (especially if they're one of the local DPEs), I'd call that a plus.