They're all related and not related at the same time... If you have any experience with any of these, please post you thoughts on them! Quite a lot of options
Diamond BoostEQ Demeter Midboost Homebrew Electronics Uno Mos Earthquaker Devices Black Eye Keeley Katana Rockness SHO clone Retro Sonic Boost Plush Pure Gain Clinch EP-Pre
I've only tried a SHO on out of that lot... not a bad boost, like the dirt at the top end of it, would only buy a clone as you say as it is not worth what Z.Vex charges, perhaps get one with crackle modded out of it and some find the sparkle on it to be a bit too much but this can be tamed by changing the input and output resistor to lower the impedence
Keeley Katana, good boost, large head room due to the MAX1044 chip in it stepping the voltage up which also makes it a great clean boost but I hear alot of people saying they don't like the gain on it, good build quality though.
Considered a Klon Centaur clone if you can find one? Got the MAX1044 chip aswell so gives a good boost and great overdrive.