Your iguana will probably go to the highest place in the cage that it can reasonably lounge. Make that the basking spot and work out the light placement to make it work to your advantage.
Not saying you won't need other lights or ceramic heat emitters in the cage to get the temperatures where they need to be. But, you can raise the temps using less expensive alternatives than Mega Ray bulbs.
Ceramic heat emitters (CHEs) are a good choice for bringing up the temps as they can also be used at night to keep the enclosure warm when needed.
A warm mist humidifier in it's own "cage" so you iguana can't get to it can also help raise the temps as well as do it's job of adding needed humidity.
DON'T forget that a Mega Ray bulb and ceramic heat emitters need a special light fixture to take the heat.
Like the black light domes shown here -