6 comp backup with home equipment (onsite or offsite)

[BKLounger]

I have a small office which is running 6 machines that will need to get backed up nightly. They currently run the machine off some 100mb meant for home use router. Would it be better if i just drop a small business server on the network to backup the machines each night or would online storage be a better option. They are looking to back each machine fully. To my understanding each machine has between 40gb -160gb hard drive. So I figure they would need around 750gb of storage (maybe 500gb).