My Dog Has Very Little Apetite And Has Challenges Defecating And There Is Blood In The Stool, What Is The Next Step, Is It An Ultrasound?

I have a dog that I rescued 3 months ago. She doesn't get excited to eat, I have to coax her. And she's not gaining any weight. When trying to go to the bathroom, it takes her 3 to 4 tries to get it all out and there is some blood in the stool. The vet told me that we needed to do an ultrasound and fine needle aspirate any problem areas. Is this the right diagnosis and should it cost $1375?