Okay, so €1000 over 120 months, that's another €8.34/month, plus the €15/month in electricity costs. A total of €23.34/month.

So yeah, you're not going to get those specs at that price on a VPS today, but there are a lot of caveats here.

1. 10 years is a very generous prediction for how long this cluster will last. In my experience, hardware that runs 24/7 lasts about 5 years before something happens requiring replacement.
2. Even if your hardware does last 10 years, Moore's Law suggests that it will be completely obsolete well before then. Chances are good that your Cluster's specs will be rentable in the cloud for less than you are paying for electricity at some point before 10 years passes.
3. Resource usage determines how useful the cluster actually is. Are you using all 24GB of RAM? Are you using all that disk space? If not, you're paying for something you're not using.
4. Maintenance. Especially with an HDD, you need to expect parts to break. How much do you budget for that?
5. Connectivity. Is your home Internet connection suitable for your needs? Is it worth the performance degradation your projects might have on your home network? If you subscribe to a second Internet connection for your hosted servers, how much does that add to your monthly bill?
6. Security. Are you hosting anything publicly accessible from your home network? Can you trust that what you are hosting won't provide bad actors access to your network? How much extra will it cost to segment your network to be more secure?

At least with a VPS you can rent only what you need when you need it, have a dedicated multi-gigabit network connection, and watch server specs increase and costs decrease as scalable hardware capacity improves over time, all while keeping your home network safely out of the picture.