Sticker shock. Does this seem high to you?

I'd pass.

Hmm... yeah, if admission is usually free otherwise, $20 per person does seem high, especially if three of you are NOT collecting candy. 

Boo at the Zoo (the National Zoo event) is that expensive. I guess for me - it's a special event, of course you pay more for it. It's a FONZ event so I assume they probably make money for zoo programs that way.

I'm not offended by the price tag for me personally.

Hell yea that's high.
Our zoo does Hallozooween every year. I think it's from 530-9pm. Different local company's volunteer for different sections of the zoo and come in group themed costumes and pass out the candy in that area. They get really into it. The Zoo also does their own decorations through the park. It's just regular admission price which is $8. Parking is $2. They only do it one weekend right before Halloween. It's fun, but usually a pretty big line to get in. I've taken melt nieces a couple of times.

Denver Zoo Boo at the Zoo

I had no idea some zoos were free, the one in Portland and Seattke aren't, and neither is San Diego.
Our zoo is close to that cost for a full day, so I would say it is expensive since it is for such a short time frame. The parking is shockingly high though, but I guess if the zoo is free that must be why.
I wouldn't pay it, I would rather spend the money for a fun day at the pumpkin patch and just do neighborhood trick or treating,

Woodland Park Zoo in Seattle is $19.95 for adults and $12.25 for kids just for general admission and that does not include the parking fee.

I don't think that her zoo is free per se, just that members don't have to pay an entrance fee normally.  So, the $120 she paid to become a member covers the cost of regular admission for the year.  

The National Zoo in DC is free, except for special events, because it is a Smithsonian, but parking costs big time - but all parking costs in DC. 

Seems kind of pricey to me. I'm not a big zoo fan in general, so I wouldn't spend that much for a zoo trick or treat.

I looked up the price for Zoo Boo for my local zoo. It's 6-9 p.m. The event description says the cost includes trick or treating throughout the zoo, Frankenstein's Foam Zone, a Freaky Deaky dance party, and Moonlight Magic with ___ (I'm guessing that's a magic show-no other info).

It also says that for an additional charge, you can roast marshmallows (no cost listed), take a spin on the haunted carousel ($2 per person), or take a train ride ($2 per person). The event description also says that while you may see some "night owls," most of the residents will be off exhibit/sleeping. Looks like parking is free, since there's no info. on parking costs anywhere on the zoo site.

$9 for members
$11 for nonmembers
free for children 2 and under

Those admission prices are for advance tickets. They say if there are still tickets left each night of the event, they'll be $13 at the gate.

So zoo boo advance tickets for four would be $44 (assuming no extras) at my zoo. That actually doesn't seem so bad, especially after looking at the regular daytime admission prices:

Adults (ages 13 and up) — $15.95
Children (ages 2–12) — $13.50
Children (younger than 2) — FREE
Military (with military ID) — $14.95
Senior Citizens (ages 62 and up) — $14.95

no outside food, drinks, or coolers allowed at any time

That's high. At least compared to our zoo boo we have every year. I think it's $6/person with kids under 2 being free. No charge for parking.

The only time we paid $90 to visit the zoo during a special event was during a beer festival held there and a portion of it was going towards animal conservation.

I could see it being that much at larger zoos.

I just checked the Denevr Boo at the Zoo cost and the regular daytime BATZ is free with admission, either by ticket or membership. If you want to attend a special after dark BATZ event then it is $17/adult and $12/child. These are these are the regular prices for daytime and the only difference is that members must buy a ticket for the special event. Parking is always free.

I do agree that this is pricey and yours is even more. At least the monies go to support the zoo plus they have to put out additional dollars to pay the staff that is working extra but would I be willing to put out the extra dollars for this few hours? Probably not. I am also very cost concious and feel I could probbaly find something just as good to spend my $$$ on .

I admit living in the DC area has spoiled me because the museums/zoos are free so I think that is pretty expensive.

One of our zoos (the one in the city) is always free for regular admission, but they have donation boxes everywhere for people to drop money into. This is the one that has the Zoo Boo and other fundraiser events. The other one out in the suburbs is $12 for kids under 12 and seniors, $18 for everyone else just for everyday admission. Neither zoo has paid parking. Since the one in the city is so good, we almost never feel the need to pay to go to the other one, plus it's a good 45 minute drive one way from where we live so that makes us less likely to go there.

Our local free zoo does Boo at the Zoo. Tickets are $6 in advance and $8 at the gate. It's from 6:30 to 9:00 and runs 3 nights - children under 2 are free. Admission includes candy stops, several activities and games, rides (like train ride and a few others) in the attached park, and one pumpkin per admission to carve. There is also no parking fee.