We are based in Northampton and our developers head offices tend to be in the big cities - London, Birmingham etc.
The cost to advertise in two different regions is prohibitive.
We had our 4 colour logo and and contact details put onto three sides of a Vauxhall Combo van for just £225 (inc VAT)!!! Cheaper than YP and lasts longer!
Had some new business from it too, and it is professional to see on site.
We find this, and the direct approach to the site manager and sales team, the best way to get a foot in the door. If they like you, and you look professional, they will happily point you in the right direction for who to contact with your request to submit a quote (esspecially if they are not happy with their current cleaner!)
Apart from this - do a good job and word of mouth helps a lot.
Site managers move around and they like to keep good people with them!