Arguably this belongs in the Accessories and Storage forum, but that's up to the mods.
You left out one key piece of information - what are you wanting to put on that tripod? I've got two Canon cameras here - the family Ixus 700 and my EOS 20D (with EF 24-70mm f/2.8L and EF 70-200mm f/2.8L IS lenses, also a BG-E2 grip). The Ixus is fine on our lightweight Slik tripod that weighs less than 500g and collapses down small. My 20D, even with the lighter 24-70 lens fitted, is way too much for that tripod; it can only be used on my Gitzo G2220 Explorer legs / Gitzo G1275M head / Manfrotto RC2 adapter setup. The only part of my setup that ever goes on the Slik is my Speedlite 580EX.
By the talk of Av and Tv, you're using something heavier than an Ixus 700. However, you'd maybe get away with a lighter tripod for a 350D and kit lens than you would for something like my setup. Unfortunately, with tripods, you can only have two of light, cheap and robust. If you give details of your equipment and budget, you may get some more helpful advice. Your height is useful as well.
If you want something that folds up as small, you're going to be looking at a 4 section leg tripod (which will, by nature, be less stable than a comparable 3 section leg tripod) and possibly using the centre column to get to your standing height as well, which further compromises stability. 30cm is unachievable; few 4 section leg tripods are much below 50cm, and you have to add the height of the head (and QR platform if you use a separate one) to that. The Gitzo G1566 monopod, which is 6 section, is 40cm, and that only gets to 1.2m tall.
David