The 150w HQI over your 29g cube should be great. Like Krish75, I've got the same light on an aquapod 24, and it's more than enough for whatever you'll want to keep in the future. I'm really glad I got this light instead of PC. Everything in the tank just eats it up (literally) and grows like crazy!
Heat will be a bit of an issue with any MH you get. You'll probably have to ditch the hood or any kind of tank cover. But for me, I like the look of the tank with no hood, and the Sunpod is sits nicely about 8-10 inches above the tank. IMO, an uncovered tank also allows for better gas exchange at the air/water interface. Just be careful of buying fish known to carpet surf!
A small clip on fan blowing on the water's surface (either the display tank or the sump) also works wonders to keep the temperature stable. Mine is on an hourly timer so I can vary the on/off cycles for hot/cool days.
On the price, I've seen used ones for $150 but not much cheaper, and I'm not sure what a new bulb costs. With the shipping and new bulb, I'm guessing you're in that ball park.