I fished with one unit for the last 5-6 years. Had unit mounted on console where I could spin it around and see from front deck. Most times I would find structure while idling around with the big motor, drop a marker bouy and fish. I caught my fair share with that setup, but like you, I really wanted two units. And, like you, just couldn't justify dropping the hard earned cash that always seemed to be needed somewhere else.
Then along comes the Helix lineup! Within the last 6 months, a lot of the HB owners have started bailing out in anticipation of the newer advanced units hitting the market. This has brought prices down on some awesome used units. I bought a used 899 from the CC classifieds and now have it on the console and my old unit on the front deck. Finally got to try it all out this past Wednesday and it was awesome.
So.....be patient, you can catch plenty of fish with one unit; and prepare to pounce on a good deal when you can afford to!
Good luck and God bless.
TerryD