So you have looked at the spring/shock options, and dicided you must get some cheap coilovers? They can be bought for sub £200 on ebay, and I get the impression that a similar product is sold under a variety of names at a variety of prices. Second hand kits are frequently sold too, and may offer an inexpensive solution, and even the chance to get something of better performance.
Im dont have any reccomendations tho. I had a golf with Jamex coilivers on it (a cheap brand) which were harsh, but worked ok. My current bilstein shocks and springs are better tho, providing more balance.
good luck in finding some, but do you really need them now? Can you make do with what you have and get the rust issues sorted before another damp wimter rolls in?