I just debated this exact thing last fall. I really wanted a full encapsulation of my crawl space, but the price was crazy. I only have a 900 sq ft crawlspace and encapsulation came out to $13.50 sq ft. I live in Western Washington (Seattle area), so we do have a decent amount of rainfall and wet conditions most of the year, but with a fully vented crawlspace I have never had any issues with humidification or water in my crawlspace.

I decided against using a closed cell spray foam for the joists, not only because of the price, but also the horror stories I have read about the possible problems with off-gassing that has plagued the industry for years. I probably wouldn't be unlucky enough to be "that one in a million situation, but...I am Murphy's bitch sometimes. One bad install and you are never removing the spray foam to try it again.

I will use closed-cell for tight, hard to reach areas, or for the rim joist bays to get a 100% seal, but not in the open bays.

I got 3 quotes from different companies and ended up with , $900 for a 10 mill vapor barrier, $3,600 for the vapor barrier and R30 insulation in the floor joists, and $12,000 for Vapor barrier, floor insulation, R10 rigid insulation on the stem walls, 100% sealing, and installing a dehumidifier (electrical work was not included as I have dedicated outlets in my crawlspace already).

So $1.00 sq ft for 10 mil Vapor barrier$3.00 sq ft for R30 floor insulation$9.00 sq ft for rigid insulation and full seal (but also includes the cost of a dehumidifier...roughly $1100 is my guess)

https://imgur.com/a/T2LyCsX

I decided not to do the encapsulation and just did the vapor barrier and floor insulation, and then wrapped the exposed plumbing in neoprene insulation after the crawlspace company was done. I am still considering installing the Rigid insulation and sealing the crawlspace up myself this year.

I talked with 3 different crawlspace companies in my area and got the same basic answer, and roughly the same pricing. All three said they almost never do full encapsulation in my area unless there is a water problem in addition to the insulation need. I dont know if this is true, but I got it from 3 different sources that could have had an easy upsell, but they all talked me out of it. It could be with how busy companies were last year, but I am leaning towards believing them.

One thing 2 of them brought up (and I found in my online DIY researching) was if you do a full encapsulation you need to provide conditioned air from the living space down into the crawlspace and let it recirc back up into the house (if you are 100% sealing) to get the benefit of a true air-insulation barrier in the crawlspace. I've redone the floors in my house and have been sealing every crack in the floor prior to this, so now I would most likely need to cut holes somewhere in my floor to provide supply and return air to the crawlspace. Not a big deal, just something I have been reading about. You also need a dehumidifier down in the crawlspace and there is maintenance to think about on that piece of equipment as well as power and probably hiring and electrician on top of the install.