Well, you certainly won't starve to death working for either English Unlimited or ELS-Bell. But you won't be looking at taking home anything more than 3,000zl per month (i.e. £600). Expect to pay at least 1,500zl for a liveable two-bed flat near the city centre. Even if you supplement the income with some private lessons, it's not going to be a good lifestyle, or even an easy one, unless you both work full time teaching EFL.
This is fairly accurate. I work for Bell and take home about 3500zl a month, from which I pay 1400zl for a two room flat in the Old Town, plus gas, elecrticity, internet, and health insurance. I sub-let a room to a cllege student-we both like the arrrangent and have been sharing the fkat for two years. That's another 500zl a month. I also teach private lessons, and that brings in another 1200zl or so a month. So I guess I get about 5000zl nett a month, less expenses for the flat, and in June I'll get paid for a lot of overtime this year. I don't live a lavish lifestyle, but it's comfortable and I like my job and my school.
I'm only telling you this because you'll starve if you work for a public school and you should know that there are alternatives.