what's going on with Mitchell Mauser's ??
They have a long tradition of misrepresenting their products, ripping people off, and refurbing guns therein killing collector value. They are generally considered by the firearms community to be a company best avoided. If you want a Mauser check out Wideners.com, samcoglobal.com, jgsales.com, southernohiogun.com, or others that someone else will chime in with.
Almost everything on the market now is Yugoslavian, either the M24/47 or the M48. The differences between them is rather minimal. The M24/47 has a straight bolt handle and standard sling swivels. They were originally M24s built before the war that were refurbed after WWII starting in ~1947. The M48 has a bent down bolt handle (while not bent as much as some like the German K98k) and has a hole cut in the stock for the sling to go through like the K98k and some others. The M48s were built from the late 40's til the mid 60's. They were exported as well. The M48 also has an elm stock while most M24/47s have a walnut stock. Most people think that the M24/47 has a little better fit and finish than the M48.
There are some variants of the M48. The M48 has all milled parts, the M48A has some stamped parts, mainly the magazine floorplate. The M48B (they were still stamped M48A for some reason) had more stamped parts including the barrel bands and trigger guard. The M48BO is the same as the M48B, but has no marking indicating origin. These were made for export to countries like Israel since the Yugoslavs wanted to sell them guns (sales are always good), but wanted plausible deniability.
Generally the going price for an M48 is $250-300, and the M24/47 is ~$200, though most of them now are being sold with accessories like bayonet, ammo pouch, and cleaning kit. $400 for an M48 is pretty high, but you did say that it was at Gander Mountain where prices tend to be about 15-25% higher than normal.