i pay around 90 Pln on a meal for two with 4 or 5 beers.
There are a few nice places in the Starówka (especially the less touristy places and some in the Nowe Miasto round ul. Freta - I recommend Pod Kogutem - a hidden gem) where you can eat for much less. I was thinking of somewhere a bit blingier with a good bottle of wine and orher drinks, coffee afterwards etc. Earning that salary in PL will mean he'll probably spend time with people who do go to the more expensive places.
Thinking of the OP's question, that salary won't make him rich if he's only planning to be there for a few years. Most locals would love that salary, however they have access to long term mortgages, credit for a car etc. If the OP plans to rent somewhere nice to live, travel round Europe in his free time, go away at weekends etc (and especially if he has to pay for flights back to South America) as well as save a little, he won't feel rich - just comfortably off. If that figure is before tax, even more so.
The average (mean) salary in Warsaw is 4 thousand and something after tax (about 7 thousand before). Plenty of people live well on less, however everything depends on expectations.too late to edit, didn't see your post:
As 40zl (or 50zl) doesn't get one a meal for two in a Spinx these days
Well north of 100 with starters, drinks and a tip and much more if you have the steak or some such.