Need a picture to be sure what you have but from what you say it's a Case 087 pattern with a spey and a pen secondary blades. The reason you can't find it is that "087PE" is the abbreviated pattern number - it's abbreviated cuz there isn't room to stamp the entire pattern number on the blade. Depending on what kind of handles it has, the full pattern would be something like 63087PE. The "6" denotes bone handles, the "3" would be three blades. If it doesn't have bone handles, the 6 will be replaced by another number.
The two dots could mean it was made in 1978, or 1988, depending on what other stamping it has. Click on "Research" up at the top of the page here for all the info you've asked about. Value depends on age and condition. Once you've researched that, your best resource for current value is to find the same knife in same or similar age and condition in eBay completed sales.
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