I work with some construction companies. They are an interesting bunch

that definitely need a lot of help. If you can do some very inexpensive or free print advertising then you can try that but I highly doubt you'll get much response. I would see if you can find a builder's exchange or another construction association and see if they have networking events. That would probably be your best bet. I know here locally they had a networking dinner cruise last week.
In this industry the hardest thing is to get in with your first client. After that they'll start referring you. If you have any contacts in the industry be sure to talk to them and make sure they understand what you do and have your business cards. If you know people who work at building supply stores talk to them too. I get referrals from the salesman at one of the local supply stores sometimes -- he knows the owners of these companies really well.
You can try the postcards...I think they are a better use of your time and money that print advertising. But meeting people in the industry is really your best bet.