If you're going to do no investment of money, then you will have to invest time because in present scenario time=money. So spend your time doing manual submission to 100s of web directories, getting backlinks from social bookmarking sites, exchanging links with websites in the same niche and so on.
So by the net
PR update (probably in the first week of September), you mighthave a decent pagerank. The rest as they say, would be history.
