Copy writing for direct mailing leaflet fo a Sales Training company B2B

We are a small Sales training company who work in the construction industry designing and delivering in company bespoke training programmes .We now want to mail all potential/existing clients in the construction industry with an offer for open courses that we want to run in April/May there are four in total. These will allow companies to train small amounts of sales staff without training all the team, which will save on cost( training budget have been cut a lot this year) whilst still offering training delivered by a company who understand their market and can bring not only skills but knowledge to the session. To help with the current climate we want to offer 2 for the price of one (may not be worded in this way)
We want to send a cover letter to HR, Sales Directors, MD, Training Managers and include a professional flyer? Can you help please? We know what we want to say but not how we can communicate this effectively to grab the interest of the reader and get them to take action. We would like to work with someone on a regular basis so they get to know our business and how we work for future projects we have planned.