Nose Wheel Tire Problem

My 415-c Has a 500x4 nose wheel tire. Most Ercoupes I've seen have been converted to a 500x5. I'm on a limited budget and the only 500x4 on the market now is almost $200.00 plus $125.00 for the tube. I feel I'm being ripped off at these prices. I have found a 400x4 for 59.95 plus tube. Any question replacing the 500x4 with a 400x4? I don't see a problem but thought I would check. Regards, Larry