UPDATE 11/21/15 I know of 23 full sized boxed fantasy toy soldier playsets sold in the 1980s. I just found a Toyco playset called Dragons and Demons that I had never seen before. It is an all English box which I have also never seen before from Toyco, except for the Tower of Terror small playset. I have installed the new playset as no. 3 on the list. So, let's say it is 23 and counting.
They are all rare. DFC's Dragonriders of the Styx is the most common and you still only see 5-10 of them on ebay each year. The scale is really from rare to insanely rare. I found the last playset I was searching for recently, ending a 15+ year search. I did not even know that a few of the playsets on this list existed until they popped up on ebay. Years of experience has given me a good idea about how rare they are in relation to each other, but there is no data or science behind my list. This is based entirely on gut feelings and a few leaked NSA documents.
I have added my best estimate of a value range for each playset. The fact is that you can still sometimes find this stuff cheap at garage sales, thrift stores, flea markets and the like. If you go looking on ebay and other places that sell to collectors you will have to pay more, particularly for items in very good to mint condition. My value estimate is mostly based on what I have seen on ebay over the last two decades. However, if you hunt for this stuff and are patient you can find better prices than what I have estimated.
Here is a list of all 23 1980s fantasy toy soldier playsets in my best guess at rarity order:
23. DFC: Dragonrider of the Styx. ($75 - $125)
22. HG Toys: Sword & Sorcery (Medium). ($50-$100)
21. DFC: The Tower of the Night. ($50 - $150)
20. DFC: The Forest of Doom. ($50 - $150)
19. Marty Toy: Galaxy Warriors Electronic. ($85 - $125)
18. DFC: The Fires of Shandarr. ($75 -$150)
17. HG Toys: Sword & Sorcery (small). ($35 - $50)
16. DFC: Giant Castle Playset. ($90 - $125)
15. Tara Toys: Dark Adventure Playset. ($75 - $150)
14. Helm Toy: The Castle of the Three Headed Dragon. ($100 - $175)
13. Miner: Dragon Crest. ($50 - $100)
12. Helm Toy: Demon Mountain. ($75 - $100)
11. Toyco: Tower of Terror. ($100 - $175)
10. MPC: Mysterious Castle. ($150 - $300)
9. HG Toys: Sword & Sorcery (Deluxe). ($175 - $300)
8. Toyco: Demons & Dragonriders (store version). ($150 - $300)
7. Marty Toy: Galaxy Warriors Non-electronic. ($75 - $150)
6. Toyco: Demons & Dragonriders (catalog version). ($150 - $350)
5. DFC: The Demons of Castlelon. ($150 - $350)
4. DFC: The Dungeons of Castlelon. ($175 - $350)
3. Toyco: Dragons and Demons (English Box). ($175 - $350)
2. Durham Industries: Fantasy Fortress. ($350 - $500)
1. Helm Toy: The Fortress of the Wizard King. ($200 - $600)