Short answer is probably not, it depends.

If you have a printer set up and ready to go, it certainly can be. But for me to get a printer and all the fixings (printer, cure/wash station, resin, tent and ventilation for fumes) I was out about 700 Cad. And then you gotta get stls, some are easy others are way harder. Some of those are free and some are paid. And then I myself am paying for lychee pro, so that's around a Netflix sub down the drain. Once that's all clear there is the insane time investment. I can easily spend 30-60 min processing a job and prepping the printer for the next print. Finding, prepping an stl to print if everything is good can take as short as an hour, but can take much longer if things are hard to find, or if it's a complex object to support. And then if you fail that print, all that time and resin (not too terrible, my large prints are like 5 bucks, small minis are under a dollar) is wasted.

After all that, there is still things I plan to buy. I lack the patience to try printing void dragon c'tan, and there's only one source that I could hope to buy a decent imotekh stl, and it'd be more expensive than buying the model (I regret buying it. That is the first and last time I ever get a finecast model).

For me the fun is in the journey not the product. I've had a lot of fun printing my necrons. I don't plan on playing in anything official, just friends so that angle isn't an issue. I went into it wanting to take up 3d printing as its own hobby and I do not regret going this route, but building a single 2k army like I plan to is not worth it. Past that I imagine the savings will roll in, but I don't really care for another army. Ethics wise I'm happy to vote with my wallet by diverting money to printing VS. paying for overpriced models.

I'm not sure if that's viable for 40k. You might not be welcomed to play with fake minis. You could surely do that with friends though.

My understanding is that you're only allowed to play what you own, no stand ins.

Onepagerule is cheaper.