Planes are low power to me because they are mainly Nitro not battery a few electric gliders are the exception. As for yachts if you buy second hand there not that bad
http://www.mya-uk.org.uk/forsale/forsale_1m.html but a new Graham Bantock special (the rolls royce of the model yachting world) it is 2 - 4 thousands for a beautifully high quality moulded boat.
Thanks for the advise its a long time since my early days membership at Donisthorpe back in the late 80's early 90's and the SX seemed like a good excuse to get back into it.
I will give this Lipo thing a try and stick to hard case type