It depends if you actually want to be a professional artist or you just want to dabble and sell on the side.
If you want to be a professional artist, then you'll need to sell your work through a gallery ( there are millions of folk just flogging on the internet)
And then I would be guided by what the gallery thinks your worth is, but getting one to take you with no track record is almost impossible with an unsolicited approach.
Watercolours on average don't make as much as oils/acrylics
And it's SO bloody hard, I'm not trying to discourage you, but you need to have an idea of expectations.
If you did portraits, and were quite good, then you might get a decent amount of traffic from that. Landscapes, not so much, but people do like local views.
Abstract, people just tend to buy something at a lower price level that matches their decor and taste, so quite restricting.
But I would say that anyone who isn't professional and wants to sell should be looking to start at under £100 to low hundreds. Regardless of how much time it took you or how much you spent on material.
There are just so many people out there dabbling, but that's just where you could start, and then if you're good and people like you and you are VERY good at working on self promotion EVERY day then you could start to gather a following.
I mean all social media, small art fairs, a blog, constant new work, constant networking with any person who might be able to help you out,
So in summary!!! It's fucking hard work, but if it's what you really want to do as a profession, then go for it, but you have to really want it, and you have to put everything into it.
Phew, sorry that was long, but as you can tell i am in that game!!!