English to Spanish Bus/Financial Business/Commerce (general)

No entiendo esta expresión en este contexto:
http://www.ce-pro.com/magazine/article/3653.html
Not long ago, the custom industry was a cottage industry dominated by craftsmen. Today, as you look at the 2004 CE Pro 100, it's not hard to see the presence of large hybrid retailers, electrical firms, security companies and even HVAC contractors. But the bread and butter of the industry continues to be entrepreneurs, with median gross revenues of $624,000 in 2003, according to the Electronic Industries Business study done by EH Research last year.