Disclaimer: I'm an instrumentalist, not an audio engineer; I'm writing from my consumption of sound systems, not experience running them.
Let's agree that the ideal, if you had unlimited funds and unlimited time and space to transport and set up gear, would be in-ear monitoring with a system like Aviom that gives each performer direct individual control of their own mix, with their own personal unit to adjust the level they get of every signal. These are often paired with in-ear monitoring, but as far as I know there's no reason they can't be used with wedges, or that the "old way" can't be used with in-ear.
There are probably many other benefits of this kind of system, but as a performer, the main thing I experienced was "cutting out the middle man." In the days of wedges, I always had to bug the sound guy for "a little more of me... ok, a little more yet... well, maybe that's too much... Oh holy crap the guitarist just showed up late and plugged in and he's incredibly hot, can you pull him way down?... well, I didn't mean all the way out of the mix..." Multiply that times each person on stage, and it makes for a very long sound check, and invariably I'd wind up just shutting up and making do with something less than ideal. This issue, of control, is separate from the issues of in-ear monitoring vs wedges (you can't both get your mic hot enough, hear enough of yourself, and avoid feedback).
Now, as far as I know, there's no reason you couldn't use in-ear monitoring with the "bug the sound guy" model. As long as the mixing board has enough aux sends for everyone, you simply run those to the stage and plug in in-ears where you would have plugged in wedges. (Plus probably some consideration that's beyond my knowledge about accounting for impedance difference.) Price: difference in price between wedges and in-ears. Bulk of gear: reduced since you don't need wedges.
I have a feeling you're looking for even more creative solutions, though. "Get the drummer to play quieter" is good for a laugh. Jokes aside, sometimes this suggestion betrays an ignorance of genre (not looking at you, Tim, more at actual conversations I've had). Someone says "Well I know it's possible for a drummer to play quietly enough for the space and for the rest of the band; I was in a coffeeshop the other day and there was a jazz combo and the drummer was just using brushes, it was so delicate and tasteful!" And doesn't recognize that if you're working in a pop-rock, vaguely Blink-182 context, it's essentially a different instrument, just as much as the coffeshop's upright bass is from the electric.
I've always found that the solution that fits the room and the style best is to fully enclose the drummer in a drum shield—you know, Lexan around the front and sides, padded panels behind and on top. Then the drummer can wale away to their hearts content, the output can be miced, mixed, and balanced perfectly to suit the space, and the monitors can contain as much or as little of the drums as needed. These shields certainly cost something (and might mean buying more mics as well, which at some point might start meaning a mixing board with more channels), and they certainly take up some space and time to lug around and set up, but still less of both than an Aviom system.