It's very difficult to generalise regarding ROVs are there are so many different types and sizes.
http://www.f-e-t.com/our_products_technologies/subsea-solutions/rovs-work-class/
http://www.f-e-t.com/our_products_technologies/subsea-solutions/rovs-observation/
http://www.seabotix.com/
http://www.videoray.com/
http://www.ac-cess.com/acrov-theacrov
And that's only a few
Martin
http://www.f-e-t.com/our_products_technologies/subsea-solutions/rovs-work-class/
http://www.f-e-t.com/our_products_technologies/subsea-solutions/rovs-observation/
http://www.seabotix.com/
http://www.videoray.com/
http://www.ac-cess.com/acrov-theacrov
And that's only a few

Martin