How to make magic items more common?

[mlangsdorf]

You're running into a problem that the original enchantment prices are extremely arbitrary (as you note), but that fixing them is a lot of tedious work. And while other people are willing to advise you on how to do that tedious work, we're not going to do it for you.

You have a pretty good idea for how you want enchantments to be priced in the abstract (roughly equivalent to equivalent TL7 technology), now you just need to go through the books and figure out the details.

ie:
The Parasol spell is equivalent to an umbrella, and should cost around $3-10 (umbrellas cost $5, per HT p30).

The Slow Fall spell is roughly equivalent to a parachute, and should cost around $1000-$5000, depending on how you calculate the trade-off between having to spend FP and not having to carry a 30 lbs of parachute.

Obviously, pricing stuff like Reverse Missile or Missile Shield is going to be much harder, because there's no real world analogue. But you can set out some sample prices for magic gear with one of those spells, and see the price at which all of the PCs buy it, one PC buys it, and none of the PCs buy it, and take some large percentage of the single PC purchase price as the price.

The big advantage here is that you're looking at end user price, not production cost. This is really how the stuff in Magic should be priced anyway, but it's not. Go ahead and correct the error while you're setting up your setting.