I am very much a museum person, and I love visiting museum shops on my way out. Museum shops are not the cheapest, but they often have a range of price points. You can find unusual items, such as reproductions of items in the museum or specialised books. They also usually have pretty notebooks and unique jewellery among the more generic gifts.
The best museum shop I have ever been to is London’s V & A museum shop. They have a wonderfully curated selection of reasonably priced jewellery and textiles. Each of their special exhibitions tends to have its own store (I LOVED the David Bowie Is shop) with items you wouldn’t find anywhere else.
I also love Stockholms Fotografiska shop because of the posters. You can buy the posters framed or rolled and some of them are absolutely stunning.

The Stockholm Dance Museum used to have their shop near where I work and I have always regretted not buying their striking jewellery featuring dancers in motion.
Another great shop is the one at the Zeitz Museum of Contemporary Art Africa (Zeitz Mocaa for short) in Cape Town. I would love to revisit the Tate Modern and the Louvre gift shops because I have not been there in ages.