Hello Peter,
there are 2 companies in Santa Maria. The bigger one is ocean properties
One staff member showed me a few appartments and she was really nice. The prices are in a similar range everywhere, so it matters most you have a seious company who cares about her name. Ocean have many different business there in sal and is a rather large one.
There is also another one with a english ownd boss. The guy in the office called Leonel and was super kind, he also take me to some appartments. Sadly i didn't buy until today because my boss only wants me to work from EU and not cape verde 
I suggest to say there for 1 year with long term rental before you decide to buy. It's complicated to sell property again and you loose money. I love cape verde, but exspecially sal & boa vista can become quickly boring.