If you don't want to worry (or care) about the water pressure or the quality of your tap water before an RODI unit the Vertex Puratek 100 GPD is the best bang for the buck. It has a pressure gauge, booster pump and TDS meter built in. It also has other nice features like automatic flushing.
I live in an split level house and don't have access to the water line or space to plumb the unit in so I just pull my unit out of the closet and make water once a week attaching it to the kitchen sink. Very simple.
I found my unit used for about $150.
http://www.vertexaquaristik.com/Prod...ek100RODI.aspx