There is not really one answer to that.
Technologically, the campaign world could be considered to be roughly the equivalent of Earth in the early 17th century. So there are still regions of the world that are deeply in the stone age. In others, they are in what we would now call the early modern period. In the most technically advanced regions, they are on the cusp of magic as technology. For example, wizard is a fairly ordinary profession in many parts of eastern Sartha and magical materials - notably fire resistant wood, cloth, and paper - are significant parts of the general economy. Various minor magical baubles and toys are available as luxury items. Magic is studied and advanced in centers of learning, and spells are readily shared between wizards of different traditions. Powerful wizards are respected and honored - though 'powerful' in my game world is like 9th or 10th level.
In the more technically primitive parts of the world, wizards are treated as criminals and must hide their profession - generally pretending to be entertainers, tinkers, and travelling craftsmen. Wizards closely gaurd their secrets, imparting only those spells taught to them to their apprentices and generally treating other wizards - if they even know any - as lethal rivals. Arcane magic is extremely limited, rare, and treated with suspicion.
To complicate matters further, the world has in three previous epochs been at higher technology levels than it is presently. The most advanced of these, the age of the Art Mages, featured magic at a level of sophistication approaching science fiction technology. So the world is littered with the relics of past ages of much greater magical attainment, the workings of which are generally unknown to present age arcanists. The reason that magic throughout most of the world is viewed with such suspicion is to a large extent the result of the excesses of these past ages. Wizardry, or 'spell casting', is in fact just one surviving branch of what at one time was dozens of fields of magical arts now lost to mortal understanding.
And to complicate matters further, it's believed by the learned that the world is on the cusp of moving into another 'golden age' or 'imperial age' where magical attaining will again soar to new heights for a millenium of currently unimaginable wonders. So while the current level of magic might be fairly low, it's not inconceivable that I'd allow a group in a long campaign to effectively advance the level of magic to some degree.
So what level of magic exists in the campaign world would depend on the location and era that I choose to set it in.
In the default eastern Sartha setting in the interum between the collapse of the fouth empire and the beginning of the fifth, the default magic level is fairly high - low magic as technology with the world generally resembling the early modern in most technical capabilities. However, because character level is assumed to be quite low, the pervasiveness and breadth of magic is generally higher than the depth of capability of magic. Magic items other than potions and scrolls are not readily available for purchase. Most non-consumable items are caster level 1 items based on 0th level spells. Items above about caster level 5 could not be made even on commission, and even those are generally available only in larger cities. Anything really potent is probably more than 900 years old, and as you reach back 2000 years or so you start encountering stuff noone knows how to make any more - like intelligent swords, elevators, batteries for storing magical energy, etc. Go back more than 3000 years and you start encounter stuff that no one alive even understands - mass drivers, dark fire, lightning throwers, sentient constructs, etc.
In terms of gear, I'd say that the level of gear I expect PC's to have is slightly less than that 3e in most respects. My characters are about 7th level and many still do not have magic armor or weapons. And there are very few 'always on' items in the game other than armor and weapons. Gear is less 'uncommon' than it is rather more random, situational and esoteric compared to 3e default. You wouldn't typically find a 'ring of invisiblity', rather you'd find a ring that let you cast invisibility 1 time per day. Most of the items that the characters have right now are on the level of 'cast a cantrip 3 times/day', '+2 enchancement bonus to a skill', 'wand with a 0th level spell', and a few magical weapons. More potent items than that often have a quirk or drawback, and really potent items always have a quirk or drawback - for example one character has the equivalent of a 'pearl of power' that drinks your blood to power itself. I consider Call of Cthulhu one of my major influences, so really potent items tend to be on the Necronomicon style face melting level.
The most powerful item in the party, and likely to remain that way for a long time, is a 'cursed' intelligent +2 keen eager rapier of swiftness that is close to being more trouble that it is worth because the character that it owns doesn't have enough will to actually control it and the sword is a little too 'eager' to kill things. At some point, it's probably going to cause the death of 1 or more PCs if they don't start treating the thing a little more seriously. The second most powerful is a silver +1 undead bane morning star. The third most powerful is probably a +1 staff of spell storing (1 1st, 1 2nd, and 1 3rd level spell).