As Andy said , 3.9M ohm is too high , use 10k to 100k . again as Andy said ,if you are using Port 0 you could simply use a pullup to the 3.3V supply for your outputs .

Also about the pricing , i have to mention you're right , but the fact is 'you get what you paid for' . IMHO AT89S51/AT89S52 are so cheap because of the huge massive production volume which is the most important key in pricing in producing semiconductors.

Using lower voltage ICs will lower 'Noise Margin' and thus you'll have to take more care on your PCB and ground routing , specially if this would be a commerciall product it shouldn't fail easily in noisy environment.

Have a nice holiday
Farshid J.H.