The Behringer 303 clone is $150 and comes with Eurorack patch points. It won't bolt to a Eurorack case... but for that price... not a bad option.

For the limited space that you have, putting gear into the rack that already has its own case is a very expensive and limiting option. They are eating up your entire case... as well as the huge, retro sequencer that doesn't really offer all that much in terms of size vs. functionality.

Which modules do you already own? I noticed the old build of the Tip Top ADSR in the rack.