I love Mountain Horse and Ariats for their comfort, but they are NOT stiff boots, so if OP is looking for a bit more structure to their boot, then Petrie or Cavallo are your best budget options. I actually ended up with Cavallo after trying a few friends’ boots - they were more comfortable for my foot. BOTH have a lot of size options - calf width, height, etc - so you may avoid custom costs if you are “Kind of” normal in the foot and leg.
I got my first pair from a mobile tack vendor, so I was lucky enough to be able to TRY ON! They had been a custom order through that vendor, then the buyer backed out - so I got them at half price (lucky me, I have a skinny, long calf - so they were not an easy size to sell, AND I got to support a local vendor). And after that, I knew what size I needed, so when I bought a 2nd pair, I got them through Divoza. There are several reputable vendors in the EU.
I still have that first pair - they are about 10 or 12 years old, and I’ve had to replace the zippers a few times now, but they are still going strong, and are my every day boot - they look a bit beat up, but not bad. Until recently, I was riding at least 2 horses (sometimes 3) at least 3 or 4 times weekly - so they were getting used.
One thing to be aware of - SOMETIMES you will get hit with customs (charged by our government for foreign goods imported). This is one reason our US tack shops are more expensive - they ALWAYS pay those customs. For an individual consumer, you might luck out and not pay. But over the years, I’ve bought most of my breeches from Europe (because I can’t find my favorite brand ANYWHERE else), as well as a pair of boots. And I’ve gotten stuck with a customs bill a couple of times. It will add considerably to the cost - so just be forewarned. Interestingly, USPS seems to be the least likely carrier for charging customs - go figure…