Update for anyone who is interested: I asked at the KLM lounge and following options were offered:
1) 389 EUR
2) 292 EUR + 13,900 miles
3) 195 EUR + 27,800 miles
4) 97 EUR + 41,700 miles
5) 55,600 miles

So one mile was calculated about 0,7 cents, making cash the preferable option.
(I cheaped out of it and am now sitting in my Y+ seat)