This is complicated question to answer. I love that you have a set number of sales though. believe it or not this helps strategizing a marketing plan so much easier (relatively speaking).

I think you mean actual home basements right? Also assuming you are in an area where basements are common. Otherwise you face a whole lot of other obstacles than growth or exposure.

With my experience and insight, here is where I would personally decide to start:
1. home improvement blogs with high reader engagement dedicated to either basements or general construction in your area only.
2. craigslist - forums. (not great, I know but people are active and that's what you want right now)
3. Create a campaign that promotes an idea like "how to add value to my home" direct that campaign to a special linked 'squeeze page' targeting those interested in value growth and there briefly, enthusiastically and in laymen terms describe how basement can double or triple in certain cases a home's value. great for those looking to sell in a year or so..? use: unbounce or instapage for this 'squeeze page' have a book now to see how long it would take for you to have your own basement. (don't mention cost here at all) focus on value, building time, etc. but not price.

keep in mind: a S.Page is nothing more than a single page used for promos, tracking ad efficiency, that is apart from your website. It should be very simple very direct. no scrolling necessary.

4. If you focus on 'making basements useful and pleasing' then go to realtors, have an affiliate system. have them sell the option for you to all their new home buyers.

this steps shoudl give you a good further follow up process.
I recommend that you stick to one or two approaches and work the heck out them. I created a strategy to grow businesses and startups particularly, dubbed it "unthink strategy," anyway this strategy shows how a company's every effort is a startup of its own and needs its own dedication and budget and goals, with any startup you can't over schedule yourself, over complicate or over itemize. Stick to one or two and go full force on them, pick a threshold to change efforts or increase efforts like after 3 sale, or if no sales are happening give yourself maybe 3 weeks or 3 months, etc.

Also, general marketing rule most don't think about: Don't contradict/undo your good marketing efforts by creating or having unattended social platforms or half-assed efforts. Is best to not have them sometimes.

Best of luck. Keep us posted maybe!

Humberto Valle
unthinkeverything.blogspot.com