Having just went though this, wanted to agree with you and leave this for others to consider:
I wasn’t thrilled with the price of the (Infratech) box either. But given I was already deep in it, I’m glad I bought, as the functionality/quality is nice. (Also a pretty future-proof design.)
With the 0-10V dimmer, I get independent control of four dual-element heaters and linear dimming through the range — it’s great. Tangent, the dimmer providing a hardwired/backup capability is nice too.
Prior to my integration, I’d bootstrapped something with $20 in parts to turn them on — FYI to DIYers, these things draw a lot of current and can interfere with other tech. if using inferior parts. For example, my LED lights buzzed house-wide at partial heater power.
Not saying it can’t be done cheaper (and props. to those who put in the research/legwork), but I think the product folks got the pricing strategy right on this one.