Good patents can't be sold at a good price, and useless patents can't be sold at a good price.
The key is how to sell it, and whether to find the demand of the other party.
Many inventions are that you don't have to find someone, and people come to you, hundreds of thousands, millions, tens of millions, hundreds of millions.
In fact, to put it bluntly is to see how much value your invention can create. Secondly, what you need to do is to know how much market demand, economic return, profit rate, operability, reproducibility, safety and monopoly your invention has. All these materials should be ready, and then your patent won't sell at a good price.