John, you seem to be hopping about from model to model- Seawolf, Hecht, Seaview, Type VII etc.
I know all the options available seem exciting, but it's worth remembering that when it comes to submarines, what you will notice most when running one, is the handling of the boat and it's reliability.
As a beginner to the hobby, what you require is a good solid boat that is fairly easy to set-up, run and transport. The Seawolf is a nice simple design and well proven, build it as standard and enjoy running it. Perhaps add a leveller.
For the next step, consider looking out for a secondhand Sheerline Akula. These crop up fairly regularly in the small ads in MMI and MB magazines, and on ebay now and again. Generally the price range is usually £200-300- the sort of price you'd pay for that pile of plastic from Krick, but instead you get a rugged cylindrical pressure hull and GRP hull.
This boat is very tough, solidly engineered, small enough to be transported easily and they're fun to sail. The ballast system is a straightforward design that requires the bare minimum of maintenance, yet works extremely well. The boats are designed and built in the UK, so parts availability is excellent, however it's unlikely you'll need much.
With a second hand purchase, you may need to replace the battery, possibly the pressure hull seals and give the hull a spruce up, but a new battery is only a few quid, and you would have to paint a new model anyway.