To help you a bit, you do need to clarify what model, the rest can be speculated on (in terms of a rough general value).
Octagonal receiver means next to nothing as mentioned, mainly because every receiver made before roughly 1936 was octagonal. The Finns used tons of pre-1936 receivers to build the various models they used and or refurbished. I don't know why many people freak out about those receivers, just something people have been told to look for I guess, even though it doesn't mean much either way.
To help the length of the gun will tell a fair bit in terms of model. Going off the top of my head the main model the Finns used were the M91s (mainly the Infantry version though there was some Dragoons and Cossacks as well) these are very long and will have a curved rear sights which is relatively flimsy looking. Then there is the M24s, M27s, M28s, M28/30s, and M39s as well. There are plenty of other minor variations, but you should be able to narrow it down to model with google with that information. From there we can give a rough price valuation and what to look for.
