The hope is that SMR will drive costs down farther in the future, these are the costs for the first one. The reason why Darlington's unit 1 (well, it's an existing nuclear plant, so the first of the SMR) is a bunch more expensive than units 2-4 is *because* it's the first, and then they've got a bunch of orders for elsewhere in Canada, and quite a few orders internationally. The hope is that serial production will drive the costs down a bunch, which will make them more attractive to buyers, which will help the cost more, and so on.
Solar's great, when it's viable, like in the southern US. It's not as viable here in Canada, not when day gets so much shorter in the winter, and the solar irradiance at solar noon is a lot less even in the summer. But even then, solar isn't ideal for base load. In order to account for really bad conditions over an extended period of time (many days of bad weather), you need a lot of extra storage. So you ultimately want a mix. Hydro. Nuclear. Wind. Solar. The more diversity the better. Here in Quebec, we're around 94% hydro and 5% wind. Ontario's about 55% nuclear, 25% hydro, and the rest a mix of gas/wind/solar.
Anyway, nuclear and hydro are really the only clean options that can provide reliable and consistent base load, and hydro is highly geography dependent, so that leaves nuclear.