For other watches you might look at Anonimo or Sinn. The problem with U-Boat, is that they are using basically an off the shelf movement from ETA and I don't think are using one of the higher grades. Nor do they do anything special to there cases (Sinn hardens theirs with a process called tegimeting, Anonimo uses DRASS on theirs). There are a lot of watches out there that you can get with the same specs as a U-Boat that cost in the $600-$1000 (US) range. So what you are paying on top of that is for how much the design of the watch speaks to you. Personally, even as much as I would love a 45mm Classico CAS, I can't justify the additional cost just for the design. Anonimo Militare Vintage is also a design I really like, but like with U-Boat their prices are not in line with the gray market discounts you can get, and they get even cheaper when they go on sale used, but I still can't justify the price compared to other watches I also enjoy with similar specifications.
Before you buy something, I would recommend finding a few different watches you like and look for them in the used forum and past auctions on Ebay. The used market can be a good indicator of retail to used ratio which I find valuable in helping to assess just how much of a premium I willing to put on getting a particular brand/model of watch.
How I went about finding watches, was to go to watch review blogs and look at what they are talking about. Also click on the links to their advertisers. I like divers so when I was trying to figure out what to get, what was out there and what I thought was reasonable to pay, I went to OceanicTime and clicked on the links for every manufacturer (after reading the reviews for the past couple years). I started in one place (also U-Boat), and then found a watch that was quite different, but that completely sang to me. Then I found another, and another, and another, and another....