Well, my humble opinion was that the axle itself should be ok. The rubbers protruding are a sign of wear and failure, but as a rule it's a very slow process, rather than a sudden failure. The arms will eventually go past horizontal and will go 'up' from the axle cross member, rather than down. As stated above, correctly, the rubbers go a long way in, so an inch or so protruding isn't too big a deal.
If the drop arms are solid (give them a bloody good thump with a hammer to make sure), then break off the flaky rust, 'kur-rust' them, give them a coat of hammerite (other brands are available
)and they should be ok for quite a while yet. However, this is the old type of Indespension drop arm - they were two pieces of steel, press formed and then seam welded together. Ergo, they're comparatively thin walled and hollow in the centre and are liable to rusting, twisting and failing. Therefore, you need to be confident they're sound.
I had to replace an axle on a Laser SB3 trailer, for the RAF Sailing Association, recently, for exactly this reason - I'll find some pics for you, so you can see what I mean.
The brakes look to be Knott 203x40 jobbies and as said prior; the studs are press-in (thump with hammer), so quick and easy to renew if required.
All the best.
oh yes - and over £400+vat is waaaay to much to pay for an OE Indespension axle.