Thanks for this post! Reaching the sub-$1000 price is very difficult for an ROV! There are a few components that just aren’t as cheap as those available for aerial drones. Most notably are the thrusters and tether.
For the thrusters, ours will work great, but you could also try to use off-the-shelf brushless motors. They won’t have the same corrosion resistance or power, but they will work underwater and can be quite a bit cheaper.
Similarly, you can start with a cheaper tether cable such as an inexpensive Cat5 ethernet cable instead of a neutrally buoyant tether.
Since you already have the basic electronics, that will keep things at a very reasonable price.
I would definitely recommend using a good watertight enclosure to make sure you protect your electronics from any water damage. Skimping there could cost a lot in the future.
I hope this helps a bit!