A big under-tapped resource is Facebook. For instance, I currently have a 1998 Double-Wide under "contract" for $6,000 and I have a place to put it.... The community yard sale pages on Facebook are a great resource. Also, direct mail and/or energizing a local lonnie dealer are also great sources for getting homes.
Expect to be all in to a mobile home for 8-12k. This is assuming you are involved heavily in the process of finding, negotiating, arranging transport, renovating, and selling. If you put someone between you and any of those processes, your cost will go up some but it may be worth it. Depends on your situation. Also, this figure is assuming you create deal flow, are involved somewhat heavily, and can get a good deal...FYI Your situation requires a lot of deal flow so you better figure that out if your budget is $10k per home.
Put the sub-meters in. I've read plenty of "great" things about RUBS, but I prefer the sub-meters personally. My opinion, probably worth it.
Your $4k per site (or $160k) seems pretty high to me. You have 12 x $150 x 12 = $21,600; I'll say you're at 50% paying for utilities so your NOI looks at best $10,800. If you are paying $160,000; you are technically paying the seller for upside. Now, my tune might change if you tell me demand is great and the market is $225+... AND, seller is carrying the paper with decent terms.