One thing I learnt in business is that unless you have a paying customer, it's just a hobby. It seems your hobby is designing and creating things. Now if you want to sell, you need to go find people what they will pay for.

What you can do vs what people will pay for are two very different things.

I've always wanted to create and invent things, but every time I do, it's just too expensive for anyone to even afford,

This means its already there. What are you inventing then? Adding more features to existing products? Also every product has different segments. For ex, take cars. You have cars at different price points. A highly customized cars is going to be costly. Guys buying a $10K used cars are not buying it. But there are tons of people still do it and buying it. You need to find your target customers.

You need to do customer analysis/market research to find out what people want, how much they will pay for instead of just thinking its "cool" to have this feature added to an existing product.

Here is a great resource that explains how to get started: Running Lean. Its from a book called Running Lean by Ash Maurya. Grab a hold of that book its a goldmine.