Is it worth it? or are there better ways to invest that monthly money? I am willing to spend 800/month on promo for my site... by i don't know what the best avenues of spending it would be... any ideas and/or suggestions would be a great help thanks in advance
$100 is a bit pricey, $40-50 is about the limit to what i'd pay for a PR7 related link. However, as i say to everyone, if that $100 link brings you $300 in extra sales it's worth it isn't it?
It's not likely the link will bring you $100 in Adsense clicks per month. Buying it for PR is a bit of a waste also, it may bring you a PR5 next update but your looking at 2 payments before the update. Assuming it "does" get you to PR5, your looking at selling 20 links at $10 to recoup your investment.. Which will in turn drain PR from your site anyway. There's cheaper and more efficent options availiable.
you can get a PR7 link for a lot cheaper than that, you just need to know where to look. But people who know are unwilling to share, so that puts you back to square 1. I would not get the link if i were you.
The PR7 site that you are referring to should also have a certain amount of traffic imo. Plus what niche are we talking about ? What is the rank of the site in that particular niche ? Homepage or sitewide or on some links page ?
It depends on the niche and the traffic. Don't forget a powerful backlink from an authority site will boost your site in the search engines.