I believe that the price is reasonable overall: it has good specs and now that FP is an established brand you know it won’t go out of business and support will last. /e/OS has become good enough lately to be reliable to daily drive (it requires some initial adjustment, but nothing to be worried about).
Also, they are phones that withhold their value in the secondary market: a used FP3+ on ebay costs more than 400€ and it had a launch price of 439€, so you can easily sell them for a good price if you ever change your mind about owning one.
The only thing that makes me hesitant to buy one is the fact that now the EU is pushing a lot of consumer friendly laws, like mandatory USB-C, replaceable batteries, extended software support and so on… So in two or three years the smartphone market might offer more high-end products that are long lasting and have a more accessible price tag. It only depends on how much time can you wait.

Edit: added links to sources