Hi Damien,
I would recommend looking into G/Flex 650. It is commonly available in Europe/UK, so I imagine that it will be cheaper there. It performs very similarly to the Loctite Marine Epoxy. We have tested it several times in our depth test chamber to 1000 meters with no leaks. The only difference that you will see is that it is less viscous than the Loctite Marine Epoxy, so you will get a little bit dripping down the cables in your penetrator (1-2 drops; it really isn’t much). If you wait about 20 minutes after mixing it, it is solid enough that it does drip. Alternatively if you clean the drip(s) off after about 20 minutes the cables will stay clean.
-Jonathan