If Formula assistance

After trying to get this If,Then to work I am stumped. Can someone please look at this and tell me what I am doing wrong?

=IF(S2<25000,R2=$100,IF(S2>25000,S2<50000, R2=$150, IF(S2>49999, S2<100000,R2=$200,IF(S2>99999,S2<250000,R2=$250,IF(S2>250000,R2=$300,0)))))

S2 contains the population value
R2 is where the amount is displayed.

I want the Then to display nothing.