When I flush every once in a while it takes as long as 15 minutes to fill in the tanK. I brought somebody to take a look at it. He suggested that I replace it with a new one for 649 $. Does that sound reasonable ?
If it's a decent toilet then just repair the defective part. A new fill valve costs anywhere between 20 for a cheapy and 75 for a commercial grade. If the problem is anywhere else a new toilet will not fix the problem. Sometimes the float rubs on the inside of the tank or on the overflow. In that case it's a zero cost repair, just adjust it to have free movement.
For a good toilet that is a good price. I install good toilets for 700 and up. Cheep toilets don't flush good.