This is a very insightful question that deserves its own article. Here is my best shortish answer. The value you provide is easiest to determine and understand as how much revenue will your work likely help generate. It’s always going to be a bit speculative. But the more experience you have the easier it gets to see how Your work helps your clients.
Here’s another way to see it. A long time ago I ran a law firm. Salespeople would constantly pitch me their products and services. Mostly I said no. At that time phone books were still a thing but I was focused mostly on my online marketing. A phone book salesperson pitched me an advertisement plan where I bought listings in different regional phone books and their online directories for different regions. Those online listings would give me back links to my site. Those backlinks would give my site SEO juice. The pitch that swayed me was one average client was worth $5,000 to me. If I got two clients a month from this plan I would get a 100% ROI. They convinced me that getting at least two clients a month was feasible with this plan.
When I do cold email campaigns for clients I know that they will likely get a 1% conversion rate, depending on industry. That means they need a big enough list to justify the cost of the campaign.
This is harder to do with content like blogs, etc. Sometimes it’s helpful to use industry standard professional rates when you don’t know what to charge. Ed Gandia has a free pricing resource that lists a range of pro rates.
As for prices in your website, I like having my prices on my site, but many gurus argue against it. I list project prices. For example an email autoresponder series will be $100 per email.
This allows prospects to see right away if I’m in their budget.
I hope that helps.