I just bought a Marlin 2000 target stock from www.e-gunparts.com.
Here's the link to the exact stock that I bought for $60.
http://www.e-gunparts.com/product.asp?chrProductSKU=925740

This stock will fit the Marlin Bolt action rifles with the clip
magazine pretty well. My Marlin 25N fit right in with only a few
modifications. I had to get longer bolts to fit the new stock and
widen one hole in the stock but that was it. I believe the barrel on
my 25N is a little smaller than the one that comes with the Marlin
2000 so I may need to glass bed it I think. I think that if you bought
one of Marlin's 22LR bull barrel bolt action guns that it might fit
this stock better. DOWNSIDE: the stock came without some of the
biathlon things I'd need like the gear to hook up a biathlon
harness/sling. I'll probably drill some holes or something like that.

Regarding target sights, I'll get the Lyman 90 MJT sight.
http://www.midwayusa.com/midwayusa/applications/eproductpage.exe/showproduct?Sal\
eItemID=863452
Some people say the Anschutz sights are way better but they're also
way more cash. You have to get the sight base to put the sight on and
I'll probably have to get a gunsmith to tap the holes. I'll probably
get a front sight as well to replace the blade on my 25N.
The cool thing about this setup guys is the price. I'm reluctant to
spend the money for an Anschutz yet but with this setup and some mods
it's not too pricey. The 25N Marlin cost me $160. The new stock $60.
New sights will be like $100 in total.

Might be a good way to get started and see if you like the sport.