I can't really speak to the balance of pricing. I would guess that they went through a variety of things and did some re-balancing. A lot of the cyberware is priced differently than it was previously, for example.
If you are changing your entire game over to 5th edition, for now, I wouldn't worry about prices being different, simply convert your gear over how it is. When you go to buy new gear, chalk up price differences as fluctuations in the market. As far as Background Count goes, that can be related to the ambient mana level increasing over time causing the fluctuations in background to be wider in scale.
So yeah, Foci are definitely still heavily influenced by background, which is definitely up to the GM to throw in and keep aligned with how they want it to affect the game. I can't think of any way for an adept to "protect" their foci. One method, as you already mentioned is pumping up the force of the foci to prevent them from deactivating. If you're concerned about losing your foci, you might look into alternatives to depending on them.
An initiated adept could also gain access to the Imbue Item ritual, which could potentially be used to increase the effectiveness of a focus without increasing its actual Force. A GM might allow the Rectitude trait also increase its resistance to Background, for example. Or allow a background resistance as a separate, new Imbued trait.
Edited (forgot to mention the comments about the adept powers):
Sadly, those ways for adepts to circumvent background don't actually remove the effects of the background. They just allow the adept to ignore the penalties. They do have the benefit that if the adept is suffering other penalties (such as from wounds), and aren't in a background, those same powers can be used to ignore that other penalty instead. Heightened Concern, for example can be used to ignore a single penalty of up to half the adept's Magic attribute. It has to be from one source, and if the penalty is too great it does nothing, but otherwise quite effective against a penalty that lingers.