Even a single family builds can vary significantly based on site conditions and required structure/design.

I recently signed up for BP and found the calculators on this site to be very helpful.  

Ask to see the approved final site plan for the first phase.

I also found a corporate housing solutions or possibly corporate express housing site that seemed quite helpful so I reached out to them as well.

But consumers all are on the site for free where real estate agents are constantly hawked to buy leads or participate in what is now a 35-40% referral business for unvetted leads who think they are contacting the listing agent.Their business model has always been flawed.

I would also look at the availability of public water and public sewer, if not at the site how far away are those services.

Have you searched your county site to identify those that have bought land in your area the past few years and then contacted them?

There are obviously a lot of variables that come into play.I'm looking at developing a small 2 acre property that has already been engineered for septic and platted for 8 mobile homes. 2 MH are already on site with all utilities present, but for the 6 MH remaining that I want to put on site, the land still has to be developed.

Quote from @Grant Francke: For those with using Buildium for property management software, do you use Buildium's public site or do you use a website you have made and maintain?

In my opinion, making an offer site unseen is not a risk.