Is this normal?
It's hard to judge from a philosophical point of view, but yes - it is normal on Allegro. The shipping cost is practically part of the Item cost - sometimes even the largest part..
What kind of shipping method you would like to advise me?
First which one to avoid: 'List priorytetowy' and 'List ekonomiczny' - these are not registered parcels and therefore often conveniently lost by post in Poland.
Which to choose - every 'polecony' - the cheapest option with pick-up at home. List polecony ekonomiczny is slower, priorytetowy bit faster.
If it's something quite expensive or you need to get it up to 48 hours get the 'kurier'/'przesyłka kurierska' and similar.
The 'In post' option is very good for clothes/shoes, etc. because you can return every Item delivered via 'In post' without any shipping costs.