I think you should just hire a mini digger and have a go yourself ,you can get the hang of it quite easy,get the delivery guy to dump the hard core in the area youve dug out ,if youre putting in a drive /cobble lock eventually you need 6-8 inches of dept of hard core,hire a large wacker from tool hire shop and this will compact it after going over it a few times ,you could use it at this stage for driving on /deliveries etc,then you could put the fine sand and cobble on later when your building finishes.its really just a bit of physical work ,wouldnt pay a fortune to get it done.