I'm wondering if company policy allows passengers, who purchased wizz priority (which allows someone to take into the cabin one bag plus a trolley bag), to check the trolley bag into the hold? I have more than 100 ml liquid in my trolley bag, and I don't want to purchase 10 kg of check-in luggage because it's far more expensive than wizz priority.
Yes, you can do this. From wizzair.com:
You will be entitled to bring one extra trolley bag (max.size 55 x 40 x 23cm, 10 kg), along with your free carry-on bag (max. size 40 x 30 x 20 cm). It is guaranteed you can bring both bags with you into the cabin area (unless it is impossible due to operational restrictions).
So you can bring it into the cabin area, but you don't have to. I have done this two or three times with wizzair. Sometimes the employee at the drop off counter are surprised that you paid for something and you don't want to use it, but they have no problem with it.
You can also use the "slow" lane when boarding and not the priority. It's up to you.