It can be quite difficult to maintain the live fire practice amount due to professional and family commitment, as well as market conditions affecting ammunition supply and price.
Some of the things a shooter can do to retain their skill level in times like these are,
1. Dry-fire: This is the easiest thing to do that won't cost any money. Trigger pull is one of the most important aspect of firing a gun and dry-firing is one of the best ways to retain the skill. It still won't replace actual live-fire, but is really better than not doing anything.
2. Reloading: It is nice to be able to shed some time from loading and being able to do it consistently over multiple times is great. Practice various reloading techniques and it costs nothing. Emergency, Speed, and tactical reloading can be practiced, and if you want to add some realism, you can use snap caps.
3. Transition from target to target: This is something you can do to enhance your multiple target shooting skills. You don't have to incorporate dry-firing(although if you can, it's highly recommended), and just focus on honing your small details.
Personal recommendation is to have 3-4 targets or aiming points and practice transitions. You can practice with two targets, but it is better with 3 or more from personal experience. You can also adjust distance away from target to account for angle you have to move.
With these kinds of practice, a shooter should be able to retain proficiency level he had before. It does require the shooter to make some time, but if you can spare 10-15 minutes each day, it should be plenty for casual shooters.
Shooting skills are perishable skills, and if you can prevent skill degradation, then you are doing well.