Well,
I'm no expert, but I do have a hoe on my B2710. My initial thoughts are:
Not industrial enough for this crowd - perhaps for any crowd
At that price, I'd be looking for a used kelly or the like - probably pick one up for around $3000-$3500 with a 6 1/2 ft depth.
How can manual stabilizers effectively stablize, unless you can manually use them to unweight the tractor. If so, then the tractor is too light to dig anything other than sand. If they are manual jacks like bottle jacks, they would be far to slow to makde the hoe useful. Ditch the manual and only offer hydraulic.
My conclusion, you won't have a very big target market with that configuration and price. If you could build a bigger, stronger conventional 3-ph hoe with hydraulic stabilizers for that price, you might have something - low cost high value producer.
Suggestions:
1 - Don't underestimate the need/importance of a correct fit and bolstered mounting points. While this is probably not important with such a lightweight hoe, if you considered beefing it up, make sure you take into account the mounting reinforcements that must match each tractor make.
2 - If you want to keep the hoe design small, I would still add the hyd stabilizers and focus on the BX crowd. That might be the best match for the size/capacity of that little guy.
3 - I still suspect that the price is perhaps $800-$600 too high. Keep in mind that most people ask "how many times can I rent a hoe for the purchase price of one?" With a price of $3000, you could rent a full-blown CASE 580 TLB 10-15 times, and the amount of work you could accomplish is not even comparable to your hoe.
I am not trying to "shoot you down". I admire your initiative. I am just trying to give you honest criticism, having gone through the process of deciding on what to buy for my needs. Maybe I am an exception, but I have read enough here and spoken with enough people face to face to suspect that most potential hoe buyers think similarly, at least in the lightweight, homeowner category.
Good Luck!