There is no reason for it to be that expensive!! Good Grief! You keep checking around because I really think you can get much better prices. I know that the shelter here offers low cost spay and neuter clinics at certain times. You might want to call your local shelter to see if they can give you any info on that.
Hopefully she just needs to be fixed and there is nothing wrong, but you need to find out. They do weird things when they are in heat!!
Keep us posted!!!