Hello, Godot Generalist Developer here,
i'm no expert, but there is a few considerations I look for when commissioning something. I must emphasize the importance of presenting things you've made in the past. I also like to see detailed descriptions of your abilities, example "i have experience with 2D platformers, 2D top down games, Finite State Machines, I sometimes make SFX and Music, and i've done some marketing" not all these skills will be related to a commission but it shows you have experience and reliability in the field.
A good way to market yourself is to make stuff frequently and post them as asset packs or around social media's, free or paid, if people like your work they will look into your other work.
Now back to your topic. Consider having different commission models. It sounds like you are a generalist if you are able to produce an entire game on your own, use this to your advantage by widening your commission models. Not everyone is looking for a whole game, some people are just looking for art specifically, or they want SFX, or Music, those are the most marketable skills on itch(to my knowledge) you may have to consider other platforms if you're looking for clients that want whole games, Itch is full of indie dev's honing their craft, there are generally more developers than artists/sound designers here. This means its hard to stand out, if your pitch is coding related.
I think, it may be more appealing to price based on how long you think the project will take, having a spreadsheet is a good start, and explaining to clients why having 50 enemies will "add x time to the project, so the cost should be reflected like so" would go a long way to making clients want to work with you.
take my advice with a grain of salt, i'm just an indie dev who likes developing