I don't have a rig to rent, but i can sell you the rig I used to use.
It can hold easily 6x R9 290X GPU's as seen in the pic, I had it fitted with 2 PSU's and a spot for the SSD (or you can use a regular HDD.)
I'ts bare right now besides the rig itself and the H81 motherboard with the CPU and fan and 4GB of RAM - also have the riser cables.
I even tried it using 3 R9 295X2 water-cooled GPU's and it was great.
Sold the GPU's but you can easily buy ones much cheaper now online then when I had this running.
I added an on off and reset cable to the mobo as well.
Let me know what you would pay for it.
thanks!
here it is naked
this is with the 3 watercooled R9 295X2 cards: