Just to make sure you understand... iSCSI is not a sharing technology. It is a disk sub system interconnect. It is equivalent to ATA/SATA/PATA. You wouldn't consider pluggin one drive into multiple machines in the same way you wouldn't want two machines to mount the same iSCSI target.
If you mount an HFS volume on two machines, you will corrupt it. The file system is not designed to handle multiple simultaneous read write masters. There are instances where you would actually want to do this however, such as high availability virtual machines. In these cases the filesystem and hosts coordinate the read/write access.
I guess you could always coordinate yourself, and mount and unmount the drive from each mac in sequence.
In a home scenario, you would normally have an iSCSI target mounted on a machine then shared out to all of the others over AFP/Samba.
But yea... It really ***** to have to pay so much for software initiators.