One of the first so called light cloud AV options was panda and that was a 70MB download for the local PC. At that time it was much larger than the PC based avast5 by some margin.
Just to let you know the current version of panda cloud (1.5.1) is 695kB.
Well I just checked that and it appears to be a stub installer, e.g. that is what does the setup and downloading of whatever files are required to be on the system as 695KB. So you would need to check what the full installation size on the system once complete.
Avast used to have one of those on-line installers when avast5 was released and I think that was tiny about 300-400KB+ and that handled the download and installation of avast on your system. That caused more grief for many with failed installations if there was a connection problems, etc.