I would recommand you to strongly hold on to it redshaddow, if not do proper search. Thank goodness you asked here. Recent Soviet mintsets have been driving like crazy and it should be worth holding onto.
For example recent auctions on ebay of the plastic sheet soviet mint set of the following are: (This is what I remembered off the top of my head so don't blame me if I am totally off but I am quite sure these prices are quite right)
1970: 600USD
1973: 150USD
1975: 250USD
It's relatively difficult to find early 1970s mintset as well as the 60s with the exception of 1967-69.
I have never seen such an external red case like yours so perhaps it makes yours very interesting, if not, valuable.
The only main reason why such plastic sheets are more desirable is simply because of the bad packaging in the hard plastic casing - most of the coins in them are toned or have some extremely ugly "metal disease" on it.
For example:

Perhaps Timofei can comment something about this - all I know is it's definately not something that appeared in the market as long as I know of these years and definately never of any sort with that red case.
Congradulations!
And for whatever reasons, please accept my apologizes for not welcoming you to the forum.