Depends on if you are using HCG or not. HCG is the most expensive, and I pay $100/mo for it on average.
Transdermals cost some money. Through insurance, Androgel and Testim should cost the same as they are brand name. My insurance has me paying $30 for brands and $15 for generics. Yours might be different. If insurance does not cover, these brand gels cost north of $400 and there is no generic version for these. Not an option, obviously.
Plus, insurance seems to be cracking down on T... I was on Testim, which worked, until insurance decided to no longer cover Testim, and I had to switch to Androgel, which didn't do diddly squat.
There is a way around that, though. Find a doc who rx's compounded creams of varying strengths. Sticker price is $55/mo, but my pharmacy has a discount if I buy 90 day supply rather than 30 day. With the discount, I pay $40/mo.
Injections are most likely the cheapest option, and I am thinking of going that route.