Poor prognosis for my boy, CT scan?

Sorry,
I don’t know if this is the right tag I just need to pour my heart out and ask for some well wishes.
On the 30th midday my baby became uninterested in his food and treats. He’s nine and has stasis once a year, I believe he has an underlying gut issue. We went straight to the vets.
By the 5th I’d ran the course of baytril and emeprid. And he was eating and happy at dinner time. But sleepy all the time.
I still had metacam so called on the 7th to see if I was to continue. They said I can stop and monitor.
On the evening of the eight he looked uncomfortable so I returned to giving him it. He took hours to finish his tea but ate all his hay overnight.
Today he ate half of his breakfast, did not touch his hay and did not poop.
Back to the vets.
He had two injections and a blood test. I was told the sleepiness is not a usual side effect and the blood test was to check his kidneys or liver.
Two hours ago I got the call about the blood tests.
Across the board, abnormal.
His white and red blood cells were too (high or low. I cannot remember). So that alone makes them suspect chronic infection that he is now struggling with.
…but when looking at his symptoms I was told lymphoma is possible. And with his age I should not be expecting a miracle and it would be a focus on comfort, or choosing to end his struggles. There is no rush to decide.
I made a vet appointment for tomorrow. 3pm on the 10th for the vet who called to have a consult. They advised a CT scan and a blood smear. I’ve paid £500 out of pocket these past two weeks and now it will be insurance. Im a full time student with a part time job, I’m not sure I can cover everything so the CT scan may be off the table. But I would feel horrendous if I put him down if it turns out the CT scan would show nothing.
Would an ultrasound be as accurate ? This was mentioned on the 30th but stupidly I declined as I believed it was his recurring issue. Not this.
I love my boy more than anything and I’m hoping with all my might I take him in tomorrow and they were wrong.
I return to university in a month, I visit him once a week while my family care for him. I feel utterly horrendous that I may be leaving my ill baby at home without me.