get that experience everyone is talking about, you just need to learn the steps and outsource EVERYTHING. With 90k:
niche research - 20$ (it's too much imo but still)
site building - 50$ (basic WP setup, plugins etc)
articles (for onsite, for article directories) - 4$ (you could get 3) x 50 = 200$
link building - 200$
(remember this is worst case scenario, you can find cheaper)
Total: $450 per site which is 90 000 / 450 = 200 niche sites, if every site is making you $10/day which it will if proper SEO (for which you pay so it better be good

) you get $2000/DAY!!!!!!!!!!!!
$2000 * 30 = that's 60k/month, ROI IS SKYHIGH.
So my advice: Spend a month reading about adsense sites, mini niche sites etc. Decide whAT to do, and be the manager, outsource everything but know what you are doing. If you don't, you'll get ripped off.
Read the forum on day-to-day basis and get the touch of how things are done. Also you'll get the usual prices. If you are stuck with something THAT IS WHY THIS FORUM IS ABOUT. We will help you out, just go out there read and try. 90k is enough to see success and good ROI (return of investment).
Good Luck
p.s. As i noticed bigger % of people read when there's a $ (the sign) involved in the post, thread whatever