I spent a few weekends digging around for this and honestly, the landscape is super fragmented. The main legal route is through Marvel Unlimited, which isn't free but is a subscription. It’s got basically the entire run, and if you read a lot, the cost per issue is tiny. Some public libraries offer digital comics through apps like Hoopla or Libby, and you can borrow 'Ultimate Spider-Man' volumes with a library card—that’s genuinely free if your library subscribes. I’ve found a couple volumes that way, but the availability is spotty and depends on your local system.
There are obviously a ton of unofficial sites that host scans. I stumbled on a few when I was younger, but they’re a mess with pop-ups, random missing chapters, and the image quality can be terrible. Plus, it just doesn’t feel right, you know? Bagley’s art deserves better than some compressed JPEG. I’d rather wait for a sale on Comixology or save up for a Marvel Unlimited sub. The convenience of having it all in one app, reading on a tablet, is worth the few bucks a month to me. Ends up being less than a single new comic.
Sometimes you can find the early issues offered as free samples through digital storefronts, like Amazon Kindle or Google Play Books, to hook you. I grabbed the first issue that way once. It’s a decent way to see if you like the vibe before committing to a purchase or subscription. Beyond that, free legal access is really limited unless you count watching people do page-by-page readings on YouTube, which is a whole other weird but kinda fun thing.