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Does anybody have experience with making a DIY practice mute? I live in a small apartment, and my neighbors name to get annoyed at even the Slightest the noise, so practicing is rather difficult. I want to make something sufficient enough to muffle my town, but not affect play ability much. Looking online at other practice music, I’d leave them running anywhere from $150-$200, and that’s not really in the cards for me right now.

I would love to learn as well

Good luck. There’s a reason why good practice mutes are expensive—besides the fact that not many are sold, so there’s little market or mass production benefit.
Ok, having said that... Start with a decent mute like the H&B aluminum symphony model. Add self-adhesive foam insulation (i.e. 1” wide weatherstripping—maybe even two layers depending on your cork thickness) strips radially between the corks—about 2/3 the way up and down near the opening on the end. The foam should NEARLY touch the inside of the bell. Leave about 1/4” gap between the foam strips and the cork. Close it up and you won’t be able to play. I used this setup for years and could play in the basement without waking the kids. And, bonus: rip all that stuff of and you have a decent mute! The self-adhesive is cheap and easy to reapply after the gig.

For me this solution works well:
I use a wooden normal straight mute (Muffled Sound, not in production anymore). I have bought a piece of 4 cm thick foam as it is being used as a filler material in the seats of chairs (this is rather dense foam). Then I have cut a circle about 4 cm wide out of the foam (with a Stanley knife), which I slide over the mute between the mouth and the lowest corks. It works good for me. Costs: a few bucks for a piece of foam at an upholstery store. If needed because of pressure, you may drill a little hole in the top of the mute, in which you have to insert a dowel or something like that, when using the mute for the original purpose.
Hubert

In high school I used to use the "poor man's practice mute" which was just my hooded sweatshirt stuffed in my bell. I practiced in the back corner of the high school band room during my lunch period while a music appreciation class was happening at the front of the room. The teacher (who was not the band director btw) was very strict about noise in her class. She never complained about my practicing or asked me to stop because she said never actually heard any tuba sound in the front of the room.

I had to practice this way at home for quite some time as well, since my dad worked the night shift for about 7 years while I still lived with my parents. I practiced with my bell pointed right to my dad's bedroom (i was on the 1st floor, he was on the 2nd) and I never woke him using this setup.

Quick tip: don't block the bell completely. I was able to adjust it quite a lot by keeping one sleeve hanging over the bell and pulling it slightly so it blocked less. It worked wonders then and I have actually tried it recently and found it to be better than my stonelined practice mute for my large tubas. For my small f tuba, it's not as good as the mute.

Don't mock it before you try it.