I would make yourself a menu, if you will, of your services. Let me explain:
First off you should decide what you want to make, or at least what you need to make. Figure out all of your personal and work-related fixed expenses; this will be the amount that you need to make. I would also multiply this figure by 15%–25% to account for the taxes you'll have to pay as a sole proprietor. It sounds like you have some data from doing this for a while, so use those to approximate how many contracts you will have on average per year (you could also calculate this per month to shorten the feedback loop and adapt your figures). Required income / average number of contracts = approximate minimum revenue per project. This figure will help you in knowing what your lower bound for a project should be.
Now obviously not every project requires the same amount of work. During my years doing consulting work, I found that clients wanted predictability because they were constrained by budgets. For complex, bespoke applications preparing estimates is very difficult. There are so many unknowns, and developers notoriously underestimate the amount of work that is necessary. My manager would usually pad my estimates with a 3-to-1 ratio.
For run-of-the-mill work though, like SquareSpace-type web projects, generating an estimate is much easier. This is where "the menu" comes in. Take one of your simplest, least bespoke contracts. Count the number of basic artifacts that that project required, such as a webpage with copy, images, standardized layout, and no custom code. Divide the minimum revenue per project by number of artifacts to yield the line item cost per deliverable artifact.
For more advanced but still routine work, like a basic database or a publishing/deployment configuration, you could list a flat cost for these line items. For these you should have templates that you can incorporate into the project without a lot of effort. For non-routine work that requires complex coding, you should list an hourly fee. If you do quality work, I personally wouldn't scoff at $50/hr; you're a business owner after all with more expenses that just your salary... But what your rate should be is your prerogative. Do some research and see what the market rate for a developer is. Don't like clients lowball you to accept a rate well below market rate.
The reason that I suggest a menu is because there is often a disconnect between the amount of work clients think a project takes and the (larger) amount of work that it actually takes. First-time clients also have no gauge on how accurate or capable you are; they might assume that you are sandbagging them with your estimate. Having benchmarks will help to manage expectations, both for you and the client. Their "order" will have less ambiguity and therefore less variability to disagree over real cost.
Disclaimer: my methodology here is less detailed than what you should actually adopt. There are many more factors, like acquisition costs or time between projects, that you should consider as you calibrate your costs for services. Err on the side of being conservative; overly optimistic predictions means you come up short when they're wrong as opposed to earning an attractive profit. But I do hope my suggestions help to frame how to think about your business model.