I would not go with a $150.00 unit from Marine depot or BRS they are too entry level and long term you will not be happy.
I recommend going with SpectraPure, but I would hold off making any purchase until you know more about the water.
Depending on the state of your source water you are going to want certain things and not need others.
For example if your pressure is constant and 50 PSI or higher then you are good, if not then the first upgrade you should consider is a booster pump and the gear that goes along with it. While not cheep it will enhance the performance of your RO/DI system more than anything else, improving rejection ratio, production rates and saving your other filters from un-necessary extra work. Get us some more details and we can help spec out the most cost effective solution for you.