The money I spent on shorts range from $50 to $600.
The rest is borrowed and volunteered.
Plus I put my time in it: sometimes weeks.
Are they perfect?
No.
Do they look half assed. No

They did add better things to my portfolio, opening new possibilities in the future and I learned a lot from it, improving my skills.
To learn to think big effectively, you need to learn small as well. Keep shorts simple: simple in concept, so you won't need a huge concept. Use them to explore ideas, to create certain atmospheres, to tell a little joke, experiment with lighting, do a hommage/parody.
https://www.youtube.com/watch?v=qeGqRVkE0AE
This was shot in one long day.
I never met the actors or makeup artist before this day: I just asked them, explained my idea AND showed my portfolio. (The caucasian male happened to be an actor who stars in many commercials, but I didn't even know that at the time. After that I can't escape seeing him everywhere on TV, billboards and in magazines, lol) Since then we worked together multiple times.
There are mistakes in this video, btw: silly things like an actor not carrying a flashlight, because I didn't write it down in the storyboard, so I forgot it at the end of the long day. ( <- This seems obvious, but as long as you haven't made that mistake, you haven't really learnt that lesson. And there a many more that you should learn before pulling off your dream.)
I paid them travelexpenses, the mua I paid extra for the use of her materials, I paid for food and the catsuit. One of my friends brought his lights. I brought slider, tripods, boom, mic and camera. I used my parents living room as 3 different locations.
It can be done.
(Ignore the licencing of the music: that did cost more than the rest. Use affordable stockmusic!)
It will cost you something, but it won't be a waste at all. It is a lot cheaper than your feature and making shorts will save your feature money, because you will make mistakes and learn from them before wasting half a million dollars on errors that could have been avoided by spending a few hundred dollars and some time.
I understand you are eager.
That is good.
Just don't bite off more than you can chew, please.
Think of short ideas that are in your grasp budget-wise, gear wise, crew wise and location wise.
If you can't rent the Taj Mahal, don't put it in the script
I've got an idea to shoot in Venice, Italy, but I can't afford that now. So I focus on other things now, that might bring that possibilty closer.
Btw, you have an interesting way of anwsering questions: it feels more like ignoring it, because you just say you understand. But how can anyone point to things you need to put some extra attetion to if you don't share details?