I mean, I don't actually need budget because I don't have a team and I'm rather young, so there's nothing I need money for. And I am actually working on a full release for the game right now, which means that I thought about what to improve before. And there actually are three things.
First, there's the art. I want to keep the monochrome art style, but I think the sprites should have a bit more detail. I think the game doesn't look bad, but it doesn't look good either. The different areas shouldn't only be differentiated through the music and level design, but also through the optics. And I really need slopes to improve the looks of the first area of the second world.
Then there's the music. You said that you liked that the music was dynamic, and that will still be a thing in the full game, but I want the music to be longer than 16 seconds at best. For some reason I can't make even remotely long music tracks, which seems to be a problem very few people have.
And since the game is only about 5-10 minutes long, I need to make the game WAY longer. The worlds in the full game are going to be much longer, each of them probably being as long as this version, and there will be 15 of them. At least for one playthrough. At one point in the game you can decide on which path of world you want to do first, and because I don't want the difficulty curve to be a mess during that part, each of them will have 3 similar versions. So there actually will be a total of 33 worlds.
Because that would take an immense amount of time, I made a level editor where I can test the levels in real time without having to wait a few seconds every time I start the game. The editor is almost ready, I just need to adjust some things to prevent the game from crashing when placing some objects.
So that's it: Art, music and length. Please tell me if you have some more questions. And thank you very much for every comment you've written so far.