The way I've been doing it so far has been difficult to manage as time went on, but easy on the wallet and not too hard to work with, as long as you are sure-handed and patient. Just duct tape (after first using masking tape, which loses adhesivity at higher temps) over string, looped over branches.
An example from early-mid December (of my now starting-to-flower plant):
Around the time I changed it to 12/12, I installed a chicken fence screen cut in the middle to allow for placement around the main stem and lower vegetative growth. With this, I started using zip ties.
An example:
I also used zip ties tied at the cross point (the X) of two terminal branches that were growing too fast on their own, so they would start to grow away from each other and more spread out. (Also because they were too high to zip tie alone, forcing me to resort to string again, of which I am currently out of stock.)
I plan on cutting my zip ties/strings in perhaps 2 weeks- I think I may use more light space if I keep them on as they stretch and spurt right now, hopefully it will do more good than bad to keep them trained that long.
nanu nanu