I never have trouble finding camps, but you can get great discounts for early enrollment. I can cut like 20% to 25% of camp costs for early enrollment. With three kids, that's a huge savings.

Some of the ones in the area you mentioned include karate and tae kwon do camps, gymnastic camps, Madeira, Congressional (they have a bus), several Montessori schools, Chesterbrook Academy, Langley School, other private schools/daycares, SACC, Falls Church and Vienna Community Center programs, and Parktakes camps. Many do not even fill up except maybe Madeira and Congressional.

You should register as soon as the camps are open for registrations. Sometime as early as in January.
Select the camps that also provide before and after care.
There aren't many selections for K or Gr.1, so act fast.

Some start enrollment in January. Some give a discount if you enroll early.

I do something similar to OP. I use my son's former day care as a summer camp for the first 6 weeks of summer. Then I pick some special nature camps (he loves nature and camping). Then some vacation time.

Day care camps are probably the cheapest option because before and aftercare hours are already included, and many camps charge more for before and after care. You can find a range of $250 to $450 a week, depending on what you are looking at.

Many have swimming, too. I wanted my son to be a stronger swimmer before going to camps that swim, which is another reason I'm using his day care camp for the beginning of the summer. No pool time at that particular camp/day care.

It depends. Do you have before/after care now? SACC has summer camp. It's easy to use, full-day, and doesn't fill up too quickly (in my experience). I would start with what's convenient for you, location-wise, and schedule-wise. We tend to pick a week or two of special camps ($$), a few weeks of vacation and time with grandma, and then fill the rest with basic day camp, most recently at the Y, since their location and hours work for us. Ask other parents at school. Many with older siblings will probably have a lot of knowledge of what's good and bad in your area.

I have a son in K this year and am starting to plan for summer. I SAH until he started K but am now working FT so need to figure out daytime activities. I've gathered people here use camps so I'm wondering what is the cost, when to sign up (do they fill up fast?), are they all day, are there specific camps that are good/better, how did you navigate it etc? Maybe this is too early to ask but I really like to be prepared. Thanks. PS. I am in McLean/Vienna