Milsurp?
+1 on the advice to buy yourself a Lee Enfield ('full woody' of
course!) It would be unpatriotic for anyone new to milsurp to NOT get one

$250-$350 seems about right for a non-rare SMLE in decent to really nice shape (as with everything expect to pay more for a superb example).
Yugo Mauser: yes, buy one! Not just 'because Marstar sells them' but because it is practically the only 50+ year old infantry rifle you can still buy in un-issued condition. Remember there won't be any newer stuff since most more modern stuff is select fire. The M-48's we have are no refurb, they're un-issued. You've your choice of matching or non-matching (sometimes new mfg. floorplates were renumbered at the factory during assembly, this explaining the non-matching ones). $400 for un-issued.
Other things to seriously consider would be an M91/30 or M44 Soviet (or other East Bloc mfg.) rifle. There's cheap ammo for them (<$200 for a crate of 780 rounds). Finnish Nagants fetch more but are built nicer. Garden variety Soviet Nagants tend to fetch around $250 in excellent condition.
Yugo M-59: a real milsurp that eats cheap ammo and is built tough. Also a good buy because it kills two birds with one stone: inexpensive-to-feed and fun semi-auto that is also genuine army issue. We have 'em for $250.
Mauser K98: as mentioned earlier we have some arsenal refinished WW2 originals. They're not in as nice condition as the M-48 rifles but have plenty of history. $400 for a decent refurb, more on the secondary market for better condition and/or all original.
Garand: pricey as a starting rifle but that's because people like Garands. Because of this they're amongst the quickest and easiest of all milsurps to sell here: when I sold one it went in seventeen minutes

Expect to pay $500+ for a decent one and almost double that for an excellent WW2 original.
In General: the three most important things to consider when thinking of purchasing a collectible milsurp are research, research, and research. To the untrained eye two apparently identical military rifles of the same model and in the same condition can be worth $250.00 and $1,500.00 respectively. The tricky part is knowing what to look for and where to look for it.
Generally speaking starting at the lower end of the price spectrum (albeit without buying 'junker' rifles) is your best and safest bet. This way you can try out several different makes and models of milsurp, sell what doesn't interest or fit well with you for (almost?) all your money back,
then focus on researching and finding rarities in your newly chosen specialty.
So long as the buyer is trustworthy and the item is as advertised you can't go far wrong plunking down $250-$300 for a Lee Enfield in decent/very decent shape, for example, but stay away from the 'super collectible' stuff until you're well-schooled in that field. If that freshly bought $750+ 'all-original matching K98' turns out to be a refurb you've just lost half your money. Worse yet, if that 'concentration camp death's head SS K98' you've paid a fortune for turns out to be a forgery you've a butchered piece of junk worth no more than $150 as a shooter

(believe it or not this HAS happened!)
Hope this helps,
- Peter