hi dan welcome to the forum,
imo only time will tell with regards to depreciation,apparntly audi might release the new version rs3 as early as this year or latest very early next year, if so thats the time when the current style rs3 with decent spec millage etc will drop to your budget much easier,but if these rumors arent true regarding early release youve got abit of a lengthy wait or maybe you will have to buy a more high millage example to stem the need but by july ive got high hopes your definatly find good ones out there to suit,
have a good look around m8 plenty of deals to be done ,personally if i had the your budget to start with and i really wanted an rs3 id hold out and get abit more together not much more and your into nearly new territory , and if you can bare to hold out you could maybe could get a good deal on a new shape when released, happy days .
good luck