No recipe here, just a tip. From late july to early september IKEA sells wonderful frozen crayfish. In Sweden there is a festivity called Midsommar and during it lots and lots of crayfish is eaten. IKEA is offering crayfish in its cafeteria and also this frozen stuff. It's already boiled in a salted dill brine and can be eaten straight away without any further cooking.
I haven't got the slightest idea why there is no fresh local crayfish sold in the Czech republic. With so many ponds and lakes there could be plenty of farmed crayfish here. The only 2 places that sell frozen boiled crayfish that I know of is Makro and IKEA but only during the summer months. This crayfish costs 249kc for 1kg. Although a bit messy to eat it's delicious with a beer or 2!