They won't stop asking until well after you stop paying. I'm not saying you do pay, but the sooner you stop the better. Tell them you're not rich - unless you are quite well off - and you must save your money for your future. 

In case you didn't think about this, it's worth mentioning that if you donate to one, you must donate to all.

Oh, and if you are extraordinarily wealthy, hide the Bentley and lie lie lie.

you foreigner, you rich, you pay. they're taking advantage of you plain and simple. don't let people fool you you "culture" 

Like everyone has said, just draw a line somewhere and stay behind it, otherwise, as you write, soon this private Red Cross / Bank of Canada of yours will find itself extended to every member of your extended nuclear family.  It can and does happen.  Really enough -- I feel for you.

I feel for you man.  They obviously think you are very well off.  Its the notion that almost all Chinese have of foreigners from western countries especially.  However, even if you weren't a foreigner they may also expect you to give as its sort of a family duty so don't get to worked up about it or think they are out to get you. 

I must say, if people cannot afford an apartment they should rent. remind them how recent the concept of private property is in this country.  If you donate, get your name on the deed.