FIRST, it should say No4 Mk1 (T) on it. Then there are quiet a few details to look for after that. A bunch of these are floating around and they are legit.
Could go as high as $800 depending on condition and how bad someone wants it. $400 was the going price years ago. $600 would probably be the right price....again, condition is everything.
I have heard reviews from "OK" to "Total junk" on the repop scopes and mounts. I believe Sarco even scrapped some of their mounts due to poor quality.
Real scopes and mounts show up from time to time for around $1,500+ but I haven't seen one in over a year (not looking either).
In the end, the complete rifles go for thousands and numbers matched sets go for thousands more.
My opinion, throw it out at $600 and let someone else deal with getting it right.
I own firearms not to fight against my government, but to ensure I will not have to.