If Christian need a priest in the church what would they say in the ad
You are make a false comparison. You didn't ask for an imam. You asked for a muslim who is fluent in Polish who would read from a pdf. That's all.
Besides there are laypeople with degrees in religion and theology studies (which includes islam) if some understanding is needed about what is being narrated. Even places like Oxford and Cambridge offer such studies but given your derisory pay for the project you are highly unlikely to attract such talent.
It's noteworthy too that you dodged answering how long the recording will be. There are videos on youtube of nothing but a narration of the quran and they last anywhere from 10 to 12 hours. So really, you only want to compensate someone £200 for potentially £1000 - £3,600 worth of work. That's stealing.
You really are taking the Hadith passage "Allah would provide for you as He provides for the birds" way too literally because your offer really is for the birds. And what's worse is you can't even buy a parrot for £200 nowadays.
Also, why are you asking for a man to do the work? What if a muslima or non-muslim woman was capable of doing the narration in Polish?
Again, you are discriminating and it is unlawful.