Hi!
Yes, I am currently using Lexmotion to file an application for my husband and children. The person I am working with has been wonderful. He responds to my emails that contain lots of questions and we even had a zoom "meet and greet". In terms of cost, we had to give a $500 deposit for them to do the document search in Poland. The balance will be paid when our file is complete. We are responsible for obtaining all the supporting documents (birth, marriage, death, etc.) but I've found I've been able to do that with no issue. 
The application has to be submitted in Polish and all the documents have to be translated into Polish, which they will do once we submit all the paperwork to them. Nothing has to be Apostilled. Knowledge or speaking of Polish is not required (which is great b/c I am applying through Romania for myself and I have to learn conversational Romanian and have all my documents Apostilled). 

I found their prices to be the most reasonable and I've priced out a few offices (some immigration lawyers in Poland and other agencies). The additional costs come from obtaining the documents (birth, marriage, death, etc. from the various offices) and depending on how many people in your family you are applying for. 

Good luck. 

Rebecca Racer
NJ