[random comment from the internet]
"You'll want our enterprise plan, an 18 month contract at $32,000/month."
Asking for money is how you turn leads into customers. You can't compete with free. If the answer to "what would you pay for X?" is $0, the person will never be a customer. Getting paid is what makes a business relationship a business relationship. It's not about never hearing "I thought you were a cool dude."
Is $32k/month too much? Who the hell knows? Not if it's what you need to have a stable business with two full time engineers able to build features for "enterprise plan" customers. Not if it adds 3x $32k for the customer.
Look, you're not "happy to build" the requested feature. It's hard work. That's why you're asking for money. When you ask for money, it has to be enough to make the work worth while. $32/month isn't sustainable. One engineer can't build a custom feature for each of 100 clients every month unless it just involves changing some CSS. Let alone 500 clients to get to the $16k a month level. Again, anyone who is put off by your asking for money, won't be a customer. There are a lot of people who think $1.99 for an app is highway robbery.
Good luck.