Overall I believe that you may have 3 options although one of these depends....
1. Cheapest - oil it. BUT this at best is probably only going to be a short term solution assuming that it works at all. I'd go with wd to start with ; if it worked might try a thicker oil later. Would try to install and to start with run outside the case ,; just ion case it throws oil everywhere etc
2. Simplest and with a definate result - buy a new one ( what's £20 for a few more years reliability and peace and quiet). You might be able to get one for a little less than £20 if you shop around.
3. Now this one depends on where the fan fixings are , depth of fan etc - Could you replace with a different make of 200mm fan ? ( just be careful - I found , for example, that coolermaster/nzxt/bitfennix all have different fixing points, depths etc and as I had a nzxt case only there own 200mm fans would actually screw in properly and some 200mm fans are , in fact 220mm/230mm)
Other makes are often a bit cheaper - coolermasters come to mind.
BTW the bit fennix ones I bought were thin (which is what I wanted) but are a bit more fragile than the bigger coolermaster/nzxt and are nothing like as good at shifting air.
Overall if I intended to keep and use the case for a few years I'd go for the new fan
Last observation - Antec products sometimes come with a 3 yr warranty - might be worth looking into? BEFORE you oil it