Expensive is a relative term though right? Compared to what? If you're comparing it with a Scarlett, it's still not expensive because you're not comparing apples with apples.
A used RME UC is around £500, and will still be rock solid in a decade. RME will still be supporting it and updating software for it in a decade, and it's 'all you'll ever need'. If you do get to the point where you need more, it'll be because you're at a point where another grand on more interface won't matter.
There are plenty of RME equivalents (Apogee, Lynx, Prism), but RME generally offers a lot more for less money, whilst being on a par in terms of quality and arguably better for support and software.
Once you use RME Totalmix, you'll never go back