Not sure how my experience from Germany translates to Finland, but here we go. I don't know about customs tariffs (product-specific duty), but with that high of a price tag, it's probably not nothing. Then expect import tax being roughly 20 % on the "product value", where the product value refers to whatever you paid to get the thing into the country (usually: price + shipping + unknown duties as mentioned above). Usually, the shipping provider that does the importing for you will also want some money for that (in addition to the shipping you already paid for).
Declaring lower values on the box used to be huge on ali (and China imports in general). But the customs people aren't idiots ... or, errrr, I mean, even if, they know that trick and might or might not request some kind of receipt (CC bill or something). Not sure how much of that has changed with new EU import regulation stuff(?)
Now the important bit: If the seller, by any chance, offers a shipping method with customs handling included (you pay for it upfront, that is), it's usually the best course to just take that. Often faster, potentially much less hassle and usually not more expensive (sometimes even cheaper because of whatever logistics magic they can use (and you as a private person can't)).