As far I can see, the price 7.500 per square meter in pre-war building in Warsaw is not exceptional high. I would say the price is average. Really huge prices are on Warsaw Starowka - even more than 20 thousend per sq. meter. Every pre-war building in a decent condition do not come cheap - ultimately just a few old houses in Warsaw survived the war.
Check this part of the article about the housing in Warsaw's buildings:
Prices? The discrepancies are huge. - In the last year, the lowest rate we recorded in the case of the post-war building at Grochowska Street, where the price per sq m. in a 58-meter flat was 5450 zł. Equally attractive price we saw in the case of an apartment in a prewar building at Siewierska in the Ochota district - 6 thousand. zł per sq. m (62 sq. m). We had a few prices less than 7 thousand per sq m. (eg in Praga Północ, Praga Południe, Ochota and Włochy district). And the most expensive were eg. Stara Street (a tenement from 1956 for a little more than 13 thousand zł per sq m.), and Słowackiego (pre-war tenement for 12 thousand zł per sq m.). When it comes to bid prices the highest value reached houses in Old Town (even more than 20 thousand per sq m.), and the apartment buildings - says Marcin Jańczuk from Metrohouse & Partners.
Average? Praga Północ housing prices in pre-war buildings generally fluctuate less than 8 thousand zł per sq m of residential premises (higher prices, up to approx. 10 thousand zł relate to representative locations on Praga Północ - eg. at. Floriańska, Targowa). In the city center, Mokotów, Zoliborz - they can go up to 20 thousand zł per sq m. Starówka - from 20 to 30 thousand, Saska Kepa - to approx. 18 thousand. zł per sq m.