We are working on a seastead design that will have a 40 by 16 foot living area above the water.
There will be 4 foot wide columns that are about 20 feet long going out from 
from the 4 corners of living area and down into the water at 45 degrees, which half of
each column under water.   The bottoms of the floats will make a rectangle about 44 feet wide and 68 long.
From the bottom of each column there will be 
2 cables going to the adjacent corners to hold it in place.
There will also be a cable making a rectangle between the bottoms of all the floats so we have some
redundancy in case one cable breaks.
The seastead is about 30,000 lbs I think but this is NOT a normal boat hull shape,
it is more like a tiny oil platform as far as drag.

We expect to use 2.5 meter diameter propellers on two low speed submersible mixers and solar/battery power to move
at around 1 MPH plus any help from using eddies.

I like the "RIM Drive" used in the Yamaha HARMO.  It provides a 227 lbs of thrust from 3.7 kw which is
better bollard thrust per kw than others I have found.  I think price is like $3,500 which is not bad.
Are there larger RIM Drives that have good thrust/kw numbers?  
The RIM Drives should last really well and have low vibration.
A larger RIM Drive from China at a good price could be ideal for me;
however all the links AIs have given me so far have failed.  If you think you have
a link to an actual RIM Drive, please check it.  Also, just having a duct around a propeller
does not make it a RIM drive.  The RIM Drive has the magnets of the motor around the rim
around the propeller.

The low speed submersible mixers have very good thrust/kw but they are big and heavy.
Numbers like 720 lbs on 3.2 kw.  These seem like $12,000 though a bit cheaper from China.

Please see what you can find that might be good alternatives to either of these for pushing a seastead.  
Thrust, kw, and also price are important.  

Please make a table with the following columns to compare above and what you find:

Type (RIM, Submersible mixer, ducted, etc),     Lbs Thrust,   Watts,    lbs/kw,  $ price, $/lbs-thrust,   URL