HID. Different temps for different watts?

so i've been growing with cfls for about six months and i have some nice bushes that are dying to be flowered. keeping the clfs as close as possible is starting to burn em (i had this in my last grow). i haven't started flowering yet .. it's going on almost two months of veg.
Here's my question..
For my space i would ideally need a 400 watt hps
I don't have the cash to get a complete ventilation system for it.
I under the assumption that hids genearally run the same temps.
so say i bought a 250
would that run me the same amount of heat as a 400.
i'm asking about ambient temps here .. of course i would setup a makeshift vent system. pc fans or whatever but until i get the money for a nice filter and fan setup i'm stuck with these damn cfls.
cfls are terrific and if i were more mechanically inclined i could probably get a great yeild. ( i'm using about 350 wt of cfls) but in scattered insufficient set-up.
so in short ...how do temps differ in different wattages of HIDs???

If your looking for a smaller light due to price you'd be wasting your time, 400 watt systems are only a few dollars more than 250 watters and if you go with an air cooled light you should be gravy, look for a 400 watt cool tube.

This site has great deal on pc fans too, easy to rig up http://www.xoxide.com/120mmfans.html
Check out the best deals thread, you'll find 400 watt hps setups for 100 dollars.. Give it a try

I'm not as much worried about the 400's price as i am the price for venting it ... like i said cash is tight .. do you think those pc fans can cool an hps efficiently for a 4x2x5 tent .... when ya think about it ...
i have the white ..plastic shitty type tent .... it's like growing in a ziploc bag. my temps get high with the cfls .... i'm just wondering if even with the pc fans .. how many cfm's would i need to move to keep it cool in cool tube