Usually the biggest growth limiter for wholesaling initially is generating enough leads. Then once you get this down it's creating systems to accommodate a high volume of leads.
As far as ROI on lead gen I've included my results over the last while below. Take in mind my numbers are market specific and relatively low compared to some of the high volume guys out there:
COST PER LEAD (Someone calls me or fills out a form on my website)
Website SEO – 53 Leads / 6 months = 9 Leads / month @ $200/month = $22/Lead
*Targeting – None/city-wide
Facebook Ads – $30-$80/Lead
*Targeting - Poor
Google Display Ads - $258/Lead
*Targeting – Average
Google Search Ads - $271/Lead
*Targeting – Average
COST PER CLOSE
12 Through Google Search ($2,640 spend) / 12 = $220 / Deal
4 Through Facebook ($9,400 spend) / 4 = $2,350 / Deal
1 Through Google Paid ($1,240 spend) / 1 = $1,240 / Deal
I've also done direct mail which is the most targeted, but it's also very expensive in my market relative to the response rate.
Anyways in summary there's been two things that have had the best ROI in my business:
1. My SEO Website for motivated sellers, it's a carrot site - designed in large part with reference to Jerryll Noorden's material
2. Getting My Real Estate License - 80% of the seller leads that would call me were retail sellers, and as a wholesaler only there was nothing I could do to help them. Getting my license and working as a hybrid investor / realtor has allowed me to convert these sellers as well. It's also been invaluable for pulling comps right away so I can talk through pricing on the phone with sellers in real time