As well as a range of prices there are also a range of features.
IIRC there are options that allow the lens to be tilted or shifted, as well as some that give an aperture ring for newer Pentax lenses, and of course plain no frills models.
Just about all the above come in a range of qualities (I don't think I've seen a budget shift adapter yet).
There's even the option of using a focal reducer to give nearer the original FOV.
If your lenses include any without aperture rings, then you'll want a DA model or you'll be forced to use the lenses with the aperture fully open. The cheapest seem to work OK, but no doubt the build quality improves if you spend more. Tilt or shift options are less commonly used, but do add some interesting possibilities for a lot less than a proper perspective control lens.
I have a canon fd fotasy adapter that wont focus to infinity with 2 lenses. It also doesn't fit very well on the lens, so it has a uneven gap around the lens. I won't buy a Fotasy again. I also have a Fotodiox Pro adapter for Konica, which is a bit tight on the camera connection, but reaches focus to infinity on 2 lens. Fotodiox also has a guarantee to focus to infinity.
I love the Fotodiox / Rainbow Imaging adapters. I have several for Pentax K, Minolta MD, and M42 Screw mount and all work wonderfully. Average price is about $22 and the shipping is super fast from Amazon. Just make sure you check the screws (sometimes they are loose in shipping and run a clean cloth over all the surfaces just in case there are any metal burs from manufacturing (actually you need to do this with the $100 ones also).
I like to focus wide open then quickly stop down to a preset aperture just before tripping the shutter. Without aperture control, you either focus stopped down or you count aperture clicks... both of which is not ideal for me.