Hm... I actually think Ukraine is probably at the forefront of UAV development worldwide at this point (both mass scale domestic production and innovation in design / tactics).
At the beginning of the war they were using bayraktars and commercial quadcopters, and maybe a handful of officially-military-designed western drones. Obviously they drew on established technology, but I actually think at this point developing a completely new generation of UAVs is exactly what they've done (primarily in the aspect of how to keep them tactically effective while making them small and cheap so they can be produced at scale at a limited tech-tier, which isn't something the Western manufacturers really specialize in.)
I think the vital stuff they're importing is tons of artillery rounds and cruise missiles, stuff where you can't really cheap it out in the same way, but if the Kremlin starts getting hit with ATACMS munitions I don't think it's gonna fly to say "naw we found it refurbished bro, nothing to do with the West." IDK, give it time, maybe by a couple years from now they're gonna find themselves at the forefront of production of glide bombs that can reach hundreds of km after building on their exhaustive experience making FPV drones.
There's not really a substitute for putting stuff into practice every day, with a heavy heavy penalty if you don't get it right. All the money in the world won't get you the same level of solution effectiveness as that will.
They're for sure getting parts and supplies for uav from the west, but they already had uav production in the beginning of the war. Most of their UAV are just commercial products assembled to carry more weight.
You'd be surprised how modular uav are nowadays. You really just need to hook motors up to a control board and your half way there. The stuff that west is probably helping with is hardening them to electronic warfare defenses like broadcast jammers.
The complexity lies in motors, sensors and actuators and especially the software to tie it all together. I'm pretty sure they got help in all of those areas. Which is not in any way meant to minimise their own achievements.
I mean, they probably aren't't producing any of the hardware. You can pretty easily build very similar UAVs to the ones used in Ukraine just ordering through your local hobby shop.
The difficult part is in assembly, but it's about the same technical level as building a PC at home. Likely the only difference between what they have and what you can build at home is the hardware/programming they're using to jump frequencies so they're harder to highjack or shutdown remotely.