Tupperware addict here.
The best way I have found to afford it is to have a party yourself, invite as many people as you know (DH takes the catalogue and the order forms into work and will get me extra sales that way too, even random strangers on the street will do ) and then buy it. The sales from your party help add money towards your own purchase. Also check out the monthly specials, because they will often have the good modular mates collections on sale - you just have to find the right month to host your party in.