Oh God.. no ventilation

So, I was recently married and now am, the 'proud owner' of a rental property that was previously my late mother-in-law's place, built in 1936, one of thousands of those "Mile-High" bungalow-style homes to be found in Denver built duiring that era. Since we want this teensy little 800 sq. ft. place to be as 'energy-efficient' as possible (good luck to me...), I began examining EVERY possible way of keeping this place cool in our scorching summer temps, only to find out that there is absolutely ZERO ventilation in the attic. No gable vents, no soffits (or eaves at all), and no ridge venting... and now I know why this place was always an oven in the summer.
So - how does one get 'adequate' ventilation throughout this attic using what I believe may be my only option: arguably, a continuous ridge vent and one or more gable vents? If I use this method, I believe I can achieve the 'necessary' venting of some 750 sq. in. of 'free vent area' (5.8 sq. ft. if my math is correct for our area).
As I said, this place has no eaves, so there are no soffits to use as ventilation, and my only 'access' would be through the gables and of course the ridge peak. But, is this sufficient?
The 'layout' of the home is a simple little rectangle-shape, roughly 24' X 33' and I believe I may have no other options with this type of construction.
"Power ventilation" (or 'evacuation' of the space by a powered fan) in the attic does not really appeal to me as I had read a report about how this seldom 'pays for itself' considering the electrical power required to achieve much true ventilation (even if I don't quite believe or understand this...).
So here I am searching for some input on how I can get this stuffy little box to 'breathe' a bit.
As an alternative, I'd also like to consider a small 'whole-house fan' that I saw at Home Depot that is affordable and easily installed, and 'lends itself' very well to cooling this place once the daytime heat diminishes (thank God for 'Mile High' cooling once the sun goes down - those who know understand that it can fall almost 40 degrees at night around here most often). But this fan 'requires' something like 1440 sq. in. of 'FVA' (free vent area) for 'proper operation' - so that just doubled my 'FVA' requirements, right?
Or - maybe not. Since this WHF would do the same thing as a 'power vent', arguably this is NOT the case... eh?
But are simple gable vents and a ridge vent 'sufficient'? Not a lot of capacity to vent much other than the 'central area' of this attic like this... But as I am always accused of 'over-engineering' everything I do (personal fault) I might be 'guilty' of this same thing here....
Input?