Since money is an issue, I would consider the iStick over any other options purely because the battery is built in. That said, I would also recommend the iStick 40w, it is a better mod than the iStick 30, for just a little more money. It not only adds an additional 10 watts, but it also adds temperature control.
Another recommendation I would make is *if* you can afford more, then you should at least consider other options like the Sigelei 30 watt, IPV D2, Joyetech eVic VTC Mini, the Sigelei 75w mini, etc.. The issue with any of these hoI wever is that you will require additional items that will incur further costs, at a minimum these will include at least one battery and a charger. A good battery will add about $8-$10, and a fair charger will add another roughly $25 or so. This will bring the total cost up to somewhere around $55-$65 for a much better setup.
I hope this helps!