I'm building my first Eurorack system as well, after some expience with semi-modular synths and VCV rack etc.
I was personally looking at the Fully Wired Electronics Transistor Ladder Filter https://www.modulargrid.net/e/fully-wired-electronics-transistor-ladder-filter. I could be making the completely wrong choice but I quite like the sound of it, with it being a ladder filter and all. Plus (Again I could be completely wrong) but it doesnt seem overly expenisive if I don't like it in the end. From what I've seen I assume it self-oscillates.
-- timeandspace
seems inexpensive - this in itself is not a good reason to buy it though... that you like the sound of it is, though!
the description states that it tracks v/oct - which might indicate that it self resonates. or might just mean that the cut-off frequency is calibrated to v/oct... I'd contact the manufacturer for clarification before buying, if I were you, if this is important to you
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities