but they all seem to offer a parking space for 30k PLN, and I have no idea if this can be added to the mortgage or needs to be paid in cash so that will be my negotiating territory.
If it is a garage then I think there should be no problem to add it... If it is just a parking space but is somehow "fixed" to the flat (so you can't sell it without selling a flat) then there's a chance to add it too... +30k then seems to be just a marketing trick on the developers' side, If you can't buy (or later sell) without it, It's in fact not 500+30 but 530.
As for the mortgage, I'm seeing some good offers from PKO, Millennium and Bank Zachodni.
Check BGŻ, BOŚ, BPH and Getin too. They used to have good deals.
and ING still want a 20% deposit.
It's the high marza (loan price?) that's got me most worried. I never understood that idea of charging an up-front fee to lend money.
I think it's prowizja you are talking about. Marża is the fixed part of interest rate, It's WIBOR (interbank rate) + marża. It's most probably due to a fact that you want to borrow all (or vast majority) of transaction's cost and LTV is over 0.8 then. Then for a bank there's a serious risk that they won't recover all the money they lent If you stop repaying it... then once they take over the property, add the administrative costs etc. and sell it, it will be still less then the money you borrowed from them... That's why these days many banks don't lend at all if LTV is over 0.8, others charge extra (that's prowizja) to cover the additional risk. Just take a look at these online calculators (they should not be 100% trusted, might be not up to date in some cases but give the overall idea...) type in 500k as the amount of loan and 500k as the value of property and then compare it with 400k loan and 500k value of property, you should see many more banks and much better offers.
So you should check what you can do to get down with LTV to 0.8 level. It doesn't have to mean you must have 20% in cash, for example in case of secondary market Value is (at least for most banks I think) what a certified guy estimate it to be (it costs around 350 PLN to get the estimation done) so for example If you buy a flat for 240k, which was estimated to be worth 300k, you get LTV=0.8 (because 240k loan is secured on a property worth 300k) without putting any own money into it... In case of primary market in the past they were just taking the price as Value but now when you can negotiate with devs I'm not sure how banks threat it, for example If you manage to get the price down by 10%, will the value be 450 or initial 500 ? It's something worth investigating because if it is still 500k for the bank, then you have LTV 0.9, find 50k in cash and with LTV 0.8 you should find a bank not charging prowizja and offering better marża. Also ask If there are any extra costs, some banks may demand life insurance or some other shyt, while others not. Use calculators and other online resources just to initially select 6-8 banks and then visit them with your own checklist.