As londuck indicates, using the histogram only a the very beginning would establish the fundamental exposure, then all other shoots could be done simply with derivations from the original histogram result!
BASELINE
Get a gray card and set it up to almost fill your viewfinder.
Set AB so that it is a fixed 4' from the gray card.
Take a series of exposures of the gray card, using f/stops in full EV increments, at a known power setting, like 1/2 power.
Looking at the results on your PC, pick the 3 f/stops which best reproduces the gray card in brightness level. (for example, if f/2.8 is overly bright, f/4 is almost right, and f/5.6 is just a bit dark...)
Now take a second series of exposures using f/stops in 1/3EV increments, with the lightest and darkest of the best 3, to serve as the extremes.
Look at the results of the second series of shots and note the BEST exposure. (for example, maybe f/4.5 looks best).
So your baseline exposure is ISO100, 4 feet flash-to-subject, f/4.5
REAL SHOOTS
Let's assume you decide to set your light 5.5' from the subject. Shoot at f/3.2 (1EV wider aperture than f/4.5) with ISO 100 with 1/2 power! Or shoot at f/4.5 at ISO200 with 1/2 power. Or shoot at f/6.3 (1EV smaller aperture than f/4.5) at ISO200 at full power. Why do we know that?
Well, treat light-to-subject distances like f/stops! So changing the distance of the light from 4' to 5.6' is one EV less light to the subject. Changing the light for 4' to 2.8' is one EV more light to the subject. Changing the power setting from 1/2 to full increases the light by one EV; changing the power from 1/2 down to /4 decreases the light by one EV.
So you do not need to buy that meter right away! If you add lights, the meter becomes much more essential, since you start to set the intensity ratios yet the lights might be at two different distances to the subject.