I have bought and traded/sold several SVT40's
value for rarity on receivers goes Podolsk, Izhevsk, Tula (higher to lower)
Year dates of rarity 1941, 1940, 1942, 1943 mythical 1944 from low to high)
I suggest reading the FAQ that Horilka wrote in the milsurp section on this rifle as it is very informative and one of the best resources on the net, my personal goal for the rifles was as original and best fit as possible. One rifle that I picked up moved at least 1cm back and forth in the stock and if I shook it the rattle was like the whole red army. It was the only rifle I sold fast for cost (probably could have done better but sold with full disclosure at it required bedding that I wasn't willing to do).
Sometimes pure rarity is of less value than personal value. I was lucky enough to find a Izhevsk 1941 with the serial number 1980 which is the year I was born, I was looking online on my actual birthday at the time.....It also shoots amazingly well (for an SVT with the odd Grimlin)
like folks have said above as with all milsurps if possible break down the rifle to inspect the parts if you intend to use it. This is important for SVT's as parts while available are much less common than for SKS's and Mosin's at this point in 2019. Watch some video's on how to break down the rifle and you will have no trouble. It is designed to be disassembled in the field with the parts available. So using the cleaning rod and or a spare round you can break down the whole rifle. Some due to fitting issues like a little work around with the rubber mallot to remind them who's boss to.