Unfortunately, beta1 can’t be installed with 256MB RAM because it includes 36 additional source packages, which use extra memory. See https://dev.haiku-os.org/ticket/14571.
It would be nice for package_daemon to not activate them unless enabled somewhere but there is no mechanism for that (yet?).
However, nightly images (https://download.haiku-os.org) don’t have source packages and they should work.
Please try that and report back.