In regards to this possibility, there appear to be one, possibly more, Star Wars masks amongst the items being sold.
Liz's Star Wars group is known for being extremely particular about appearance accuracy. This leads to their costumes being of movie prop, or near movie prop level. The $74.99 complete "Sexy Dark Side chick" club'in Halloween costume won't work.
Prop, or near prop level costumes are expensive to buy- when the individual components are even available. As a result, it is evidently not uncommon for members to spend considerable time and effort making their costumes.
So, possible group level costume components being "garage saled" could fit your requirements of something of high sentimental value, hand made, gifted, or had been promised / perceived to of been promised to somebody.
But wait, there is more..... Having an acceptable costume can be road block to joining the group. Membership in that group can be prestigious in a sub culture that may have a certain number of participants are high maintenance in regards to self esteem, lacking other social outlets and / or are "starting over- and this had better work".