A DivX at 200meg can blow out to 1.5meg SVCD no problems there.
It all gets down to the bit rate used to make the DivX in the first place. If the pic size is made small and low data bit rate for both Video & Audio then you end up with a poor quality AVI, but small in size. In TMPGEnc if you take its standard templates asks for a high data rate for Video (and Audio) and its pic size is basically fixed at 480x480/576. The mpeg2 encoding in a SVCD is no where near as compressed as it is in a DivX.
What is the length of the DivX movie in time, thats more important than meg. You will fit about 79min of VCD movie onto an 80min CDR and about 50min of SVCD. As for a DivX on an 80min CDR, well anywhere from 30min to 3hours or more. So if you have a 1 1/2hr movie (typical length) as a DivX and regardless of its size, it will always convert to a 900meg VCD file or about 1.5gig SVCD file, with both cut in half to fit to 2 CDR's.