You're right, no filter for the 89.99 package.
I do like the aquaclears. I've had a few of them over the years, and I'm running one right now on my main tank. The C2 interests me, but I've heard that the flow is quite heavy - one review I saw said the C2 set on "low" had more flow than an AC set wide open. Do you have it? Is it too much for a 4gallon?
I'd even consider a small canister if I could control the flow and block the intake properly to protect fry/shrimplets.
I have an AC 20 and I thought the C2 used the same motor. So I can't speak on the flow of the C2 but I was considering it as an option. The Zoo Med 501 seems to be a popular canister filter for nano tanks.