MattHere is the trick to all of this. You have to be careful not to throw away all of your profit on tools and leads. If you have 10 units and do a bang up good job and sell 10 units per month, then you probably have around $20,000 gross after policy work. So now you pay Cars.com or AutoTrader $1000, Pay vAuto $1500, pay your DMS provider $250, pay your CRM $300-$500, pay pay pay...and now you have nothing left.
This a million times. It's common to go apeshit and throw money towards any third party vendor that offers you X amount of leads and X million unique visitors per month shopping right through your digital door, etc. In the end you could have cash flow issues.
Source : Small dealer my marketing firm picked up a while back, within our second month they were selling 60% of their inventory (mind you it was like 20-25 cars total on their lot). Then they decided to throw money at ATC's premium package, cars.com, cargurus, the whole nine yards. Ended up selling the same amount in that month, and had to drop us and their third party sites for 2 months because they 1) Didn't have enough cash flow to pay their bills, let alone themselves, 2) Didn't have enough capital to go to the auction and buy cars to make up for their sold inventory, and 3) Decided to pay their sales tax quarterly, which really screwed them up in the end.
The result? A terrible Q3 and they took out a loan.
For now, as a starter, i'd get a basic website going, get your business listed on Google+, Yahoo, Bing, Yelp, DealerRater, etc so you'll have some solid citation links and a local presence. Try the classifieds way first (Craigslist, $5 per ad, can't really beat that), then slowly focus on increasing your budget for networks like Cars and ATC.
Also, stay in these forums! I've been lurking here for so many years, and just started posting. So much information here to help your dealership out, and it's a network of auto pros like yourself to share ideas and strategies needed to keep up with the next-gen of dealer marketing.