Yes, you can get case fans very cheap on newegg, I bought 10 for $10 with no shipping costs.
I guess if you are really concerned you can download a freeware temp reading program that will tell you mobo temp and see if it reaches a critical value. Maybe your ASUS mobo came with the program, mine did and it is very handy.
-AMD Phenon X2 555
-Western Digital Caviar RE WD2500YD 250GB 7200 RPM 16MB Cache Serial ATA150
-Patriot Sector 5 DDR3-1333 (4GB)
-Rosewill 500W PSU