One reason for the high cost of LED lights is the extras that T5HO lights don't have. For example, dimming is very rare for T5 lights. Adjusting the color temperature is unheard of for T5 lights. Programmed brightness throughout the day is not done with T5 lights. Once you drop all of those extras, LED lights become much more economical.
One good thing to take advantage of with LED lights (my opinion) is the ability to get very uniform light intensity in the tank. That takes more LEDs, but lower power LEDs, than just replacing the concentrated light from T5s with concentrated light from LEDs. But, if you don't want to do that, LEDs certainly are already economical compared to T5s today. My preference is to give up some of that cost savings to get the more uniform light, and my DIY LED lights do that.