I'm from Finland where almost everyone who works in media belongs to the media workers' union. We have a price list which cross references the length of the gig and the job title / required experience level. It makes negotiating salaries super easy and painless. The rates are a lot lower than in the US / England though, so there's that. For example:
technician on a 2-10 day gig: 217,10 euro / day; on a 11-24 day gig: 185,56 euro / day
engineer on a 2-10 day gig: 259,91 euro / day; on a 11-24 day gig: 197,96 euro / day
designer on a 2-10 day gig: 305,00 euro / day; on a 11-24 day gig: 237,40 euro / day
etc.