hey buddy, well that answer is pretty simple. i was obsessed back in the old days of getting every release from every country and yugoslavia was surely one of them. as some of the 7" sleeves were very different to these released in the UK.
i have estimated the value based on a reasonable ebay price. most of sleeves are VG+ since they used a very thin paper back in the 70's. here you go:
1. seven seas of rhye - probably the rarest yugoslavian release. sells at approx 200-220 dollars on ebay. many of these exist with pen marks and very wrinkled sleeves (mostly at the top, where the vinyl goes out). and by the way i have one for sale at VG+ :)
2. killer queen - 2nd rarest yugoslavian. i love the sleeve. sells at approx 150-170 dollars. sleeve at vg+ to ex condition is very hard to find!
3. bohemian rhapsody - you can find many of these on ebay. i'd say average price 25-30 dollars for one in VG++ to ex
4. you're my best friend - very nice band sleeve. i'd say 3rd rarest yugoslavian. being sold for pretty cheap. i'd say around 70-75 dollars (i have 6 of these in my collection lol)
5. mustapha - was considered as mega rare like 15 years ago. but these days you can easily find it for like 80 dollars in ex condition. sleeves are very thin so make sure you don't lay your hand on a torn sleeve.
all others (somebody to love, first EP, we are the champions, crazy little thing, save me, etc etc etc) are not even worth mentioning, less than 10 dollars. LPs worth the same. i'd say up to 15 dollars. maybe sheer heart attack with special yugoslavian insert can get up to 20-25. but nothing more)
let me know if you have any question, cheers!