Propstream skip tracing is pretty bad, which is unfortunate considering I really like the rest of their product suite, and think it is a must-have software for wholesaling. As mentioned before in this chain, door knocking is an option, but it's not one that I was ever willling to do at any scale. Text and Cold call are going to be your cheapest options and probably the most helpful to start with. Because they have low conversion rates, you are going to get into a ton of conversations and deal flows to give you experience. Once you feel like you are a top-notch closer, or have hired someone who is, then jumping into the expensive but more scalable marketing channels- such as PPC - becomes a good option.
Until then, I would recommend NOT using propstream for skip tracing. Holler at me if you want me to share my skip tracing contact that I've used the past three years. He is great.
Secondly, either individually dial / text the records you have skip traced, or get going on an outbound software like Calltools for calls, or Launch Control for text. I use launch and am an affiliate partner there, so can get you some cool perks if you sign up through me. Hope this helps and reach out if you want to talk more!