£35 around $70 US per hour is the average studio cost here in the UK and that usually includes an engineer who can set up drum loops plus play keys and guitars on request. They will sometimes work on a cost per song rate if you work a lot with them and they will take your song as far as it needs to go. I get great deals because I work with them a lot. I also know a few great guitarists who will lay down a guitar part pro recorded for around £100 ($200 US) again negotiable depending on how much work you give them and how well you know them. The same with drummers and keyboar players etc.