I can tell you from my experiences that Radio is very costly for what little return it does bring, if any! I've tried Google Adwords as well and I spent hundreds on it with NO return. All I seen from it was a nice increase in traffic to my website, but not a single appointment was generated from it. Something I've done during the winter months was set up an ad with a company that prints Golf Course Score Cards. These Score Cards have multiple businesses printed in full color and depending on how popular the golf course is, tens of thousands of people with expendable money will see your ad. You can detail their vehicles while they're playing a round and when they're finished they'll be treated to a great looking and clean vehicle without having to be inconvenienced.
Like many others have said in this post, word of mouth is the absolute best advertising you could ask for! If you have money you can re-invest into your company then I'd say put it in a vehicle wrap and/or vinyl lettering on your truck/van/trailer or whatever you use. Also, I see you are looking for canopies...put your logo, ph #, web address, slogans on these canopies that way when they're set up people will take notice of it. Push your brand as much as you possible can in the least expensive ways to capitalize on revenue coming in.
Website, social media, and your mobile rig(s) should be priority #1 as far as advertising is concerned and from what I have seen of your brand thus far, you are moving in the right direction. "If you build it, they will come"