Most if not all in-company schools in Poland work throughout the year. I only take a fortnight in the summer, and not always that. If anything I teach more during the summer months because of covering for teachers who are on vacation or doing summer schools.
All English teachers don't get 50zl for 45 minutes
I don't know of any professional and qualified native English teachers in Warsaw who work for less these days. If you do, please give me their details, I could save a little money.
I'm afraid the rates for teaching english will fall dramatically in the future
If anything they are slightly rising in Warsaw due to supply/demand together with a dearth at the lower end of the market. That isn't only my opinion, it's my concrete and up-to-date experience as a school owner.
There's a much greater supply of Poles teaching English than of skilled natives, and, however good Polish teachers may be, they don't generally command the same rate per hour.