Owned my first one at around 23 and my insurance was around the 700quid mark
I've owned 5 RS Turbo's and used every one of them as everyday transport with no problems and tbh the fuel costs are more than acceptable.
As for rust, well its like any car what is 15yrs old and above, you are gonna get alot with some rust and your gonna get a lot of nails, its best taking someone who knows what they are looking at to look in all the trouble spots that are associated with a Escort.
But be patiant and look at plenty and you will find yourself a good motor