Sparkle might be what you want if all you want is a decent, modern iWeb replacement and little else. RapidWeaver takes it a step further. Try out both of them and see what suits you. Adobe solutions are probably going to be too costly if you do not design for a living.
I, for one, recently moved to Sparkle from RapidWeaver after 8 years of being with RapidWeaver and it has a lot going for it. I think, for your basic no-frills needs, you will find Sparkle a better fit for you, and the community is responsive and helpful, and the developer is always an email or a community message away.
Difference between Sparkle and RapidWeaver:
1. Sparkle is what you want if you want complete customisation. This gives you a blank canvas and you place blocks on it to design your page. RapidWeaver utilises themes, and themes offer limited customisation in the end, despite what they promise. After a while, while there are plenty of themes floating around, they all end up being similar and it is not a completely customised design.
Sparkle offers way more in terms of design customisation since not only do you get to design how your desktop website looks, you also get to customise how your website looks on mobile and tablet. This is an effort that you might enjoy, since nothing else comes close to designing your own thing out of your own imagination. You cannot place your menu in the middle of the page in RapidWeaver if you do not have a theme that has that option. Instead, with Sparkle, you just place the menu wherever you want.
2. Sparkle offers a lot of functionality out of the box that you will have to pay for in RapidWeaver. To fully utilise the potential of RapidWeaver, you will have to buy a plugin called Stacks. Between themes and plugins, RapidWeaver is a lot of investment over time and even initially, since the prices of themes and plugins have shot up quite a lot over the years. Sparkle is the clear winner here.
3. Sparkle makes it easy to design GDPR-enabled websites and almost walks you through it. The code generated is geared towards performance and SEO. RapidWeaver usually is happier with getting you to buy themes and plugins for the smallest of functionalities. You need to know code for achieving things without those plugins whereas in Sparkle a lot of functionality is achievable out-of-the-box.
I suggest you try Sparkle before trying RapidWeaver and see how they both work for you.