Decreasing size of poop is as you’re saying a possible early sign of GI stasis. It can also be just a reversible gut slowdown accompanied by gas. Too much broccoli or other cabbage-type vegs can cause gas in sensitive individuals. An individual that normally tolerates broccoli can be more sensitive due to stress, f ex the stress of being in a new environment or when routines are broken. Gas is very painful for bunnies and would explain his aggression and unwillingness to binky like he normally does.
Very light tummy massages are good, also try and elevate the bunny’s rear so gas can escape easier. Many bun-owners including myself like to give baby gasdrops (simethicone) for suspected cases of gas. Dana Krempel abnd Medirabbit say it can be given on suspicion alone. (To actually confirm gas, you need an x-ray). Simethicone is not absorbed by the body but acts locally ijn the intestines and is expelled with the poop. 1 ml per hour for 3 hours is the suggested dosage. It very often helps within 20-30 minutes.
It’s really great that he’s drinking a lot. Cutting back on pellets might not be the way to go, because you want him to eat. If he eats more hay when he gets less pellets it’s fine, but you don’t want his tummy to go empty.
How does his ear feel? Very cold ears could mean he’s got a low temp. That’s very bad for a bun, and he could need warming up.
I can’t give you any idea about cost of a vet visit, it varies greatly depending on where you are. If you tell us what country/general area your are in, someone here might have some idea. Unless the bun needs hospitalization and it’s daytime and a weekday, a vet as a rule takes an X-ray of the abdomen, gives (warmed) fluids sub-q and perhaps a painkiller and a gut stimulant, and none of that is necessarily crazy expensive.
I’m not a vet, so I can’t tell you what you should do, but when my buns have been in a similar situation, I’ve always started with the gas drops. They can be surprisingly effective.
.
