In my experience, DJ fees run from between nothing to £150, depends on how nicely you ask some DJs...
High-rollers will often DJ for very little/nothing/a sales pitch if they like the music policy or promoter.
Best advice is ask them if they're willing to do it for a smaller amount, with the option of upping their fee if it's a packer... say £30 per DJ as a starting point....
Depending on how busy they are, most DJs would rather be out every weekend DJing for a bit of expenses (read as beer money) than be sat at home charging nobody £150 for the privilige.
WOOF!