and you could use a 120 to 30 volt transformer and simply apply 120 to the 30 volt side

That you can't, the thing will saturate...

If this is permanent, I would just change the ballast. Technically speaking, lighting over 120 volts is not allowed in residential settings in the US. From the 2014 NEC:

210.6 Branch-Circuit Voltage Limitations. The nominal
voltage of branch circuits shall not exceed the values permitted
by 210.6(A) through (E).

(A) Occupancy Limitation. In dwelling units and guest
rooms or guest suites of hotels, motels, and similar occupancies,
the voltage shall not exceed 120 volts, nominal, between
conductors that supply the terminals of the following:

(1) Luminaires

(2) Cord-and-plug-connected loads 1440 volt-amperes,
nominal, or less or less than 1⁄4 hp

If the control transformer is mounted in the fixture it meets code because your feeding it with 120, what happens in the fixture stays in the fixture, but you are right just change out the ballast, it's the safest, simplest and more the likely the cheapest..

Be safe, get a new ballast

@Lodge: 100% correct. The NEC does not cover whats inside the fixture or appliance. But the amount of iron involved in boosting the voltage to 4x would perhaps be more than the ballast already inside there. Heat build up might be an issue as well, but there is no way to know until testing it.

Any pics of the fixture? Most fixtures will take retrofit ballast mounts well. With LEDs taking over, ballasts are starting to run cheap. Ebay might have a new in box ballast for less than $50. 

Those will easily take retrofit ballasts.

If this is permanent, I would just change the ballast. Technically speaking, lighting over 120 volts is not allowed in residential settings in the US. From the 2014 NEC

Add a USB charger in each so it counts as "USB charger with light" instead of "luminaire"

How about "outdoor heater"?

So far, I have been using some reverse fed industrial control and general purpose step down transformers as step up transformers in addition to split phase 240V to run my lighting that requires voltages above 120V so far. I generally use a plug on the primary side and an appropriate receptacle on the secondary side of my transformers to ensure that I disconnect power easily whenever I experience problems. I just use common sense by turning off the power whenever I need to service my fixtures or step up transformers as well as never touching any exposed live components to avoid getting shocked. So far, I have used transformers to run 208-277V lighting so far, but recently acquired a transformer that I have been planning to use for 480V lighting. In particular, I have been planning to use a 460V 60Hz 1000W H36 mercury vapor reactor ballast to run one of those hard to find 880W Sylvania Unalux high pressure sodium retrofit lamps eventually. Most importantly, care must be taken when working with step up transformers for high voltage lighting applications.

Our 3PH voltage in Israel, is 380V I think.