Nice spot. If your budget is in the $200 range hps is likely what most will suggest. If you're thinking hps, buy one of these and run it bare-bulb. They're 315w Philips Elite Agro bulbs but produce more like 450--500 hps if they made them. Definitely better than a 400 hps and in that space you could yield 12-16 zips with one of these depending on strain. They're also a lot cooler than hps so heat won't be an issue to manage in there. Only thing with the unit in the link is the ballast runs on 240v only, you'd need a step-down converter to run it at 120v.
http://advancedtechlighting.com/cdmmw.htm
If you had more budget I'd suggest COB-based LED's as they would be effective and produce nearly no heat to deal with.