My agent is currently taking up about 71 MB:
$ pwd /home/ips/Applications/rhq-agent $ du -sh . 71M .
with the following breakdown by subdirectory:
$ du -sh * 412K bin 64K conf 30M data 16M lib 12M logs 12M plugins
Note, the data and logs directories have a variable size but can be periodically purged if they start consuming too much space, and the size of the plugins directory will vary depending on what plugins you have installed.