Say you have 100+ new sites and you want to build links and get some PR - which is easiest and cheapest link building method?
Outsource. With 100+ it may be too much work for you alone. I would recommend buying scrapebox personally and just to link blasts for 3-5 sites every day.
i think you would need to buy multiple automated backlink softwares and automate the process there is no way you can do it manually
or buy signatures - very quick way to bulk up... might get penalized though - but yu might get that from automation too
It always dwells if you have enough budget to blast your links in short span of time but I prefer doing it myself to be sure I get quality links.
100+ is a lot of sites. Maybe you can use xrumer profile blasts but they are usually good only for the short term. Joining some link network maybe good too