It's really an interesting idea to keep mining rig cool during the summer

But here is some of my concern, I might be wrong in doing my calculation coz I've never dealt with datacenter space rent.

From data you provide,

1U rackspace comes with 90W of power costs $20/Month, I only consider in terms of power supply (not space in the rack) ATM,
in order to power a 4-video cards ming rig, it requires 7-9 blocks of 90W depends on cards, so that is $20 for the first 90w block plus another 6-8 90W blocks @ $15/each, that's about $90-$120

So only power supply will cost around $100/month/rig

Now, get back to space in the rack, a full size video card is about 5 inch and a typical 2U is about 3.5 inch, I don't know if there is enough space inside to accommodate a typical 4-video cards mining rig.

For ppl who are using FPGA might be a good idea?