Average Cost Of Laparotomy Type Surgery?

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Can someone please give me a rough idea of how much it costs to have exploratory surgery? (on a largish dog-around 30kg). My dog is sick again (had the same symptoms about a month ago) so we are currently awaiting results of blood tests but there is chance we may have to do surgery to see if anything can be found in abdomen that explains his problems. Just wondering what people have paid in the past for this sort of surgery?

Thanks