I bought this one this morning. Newly certified. Pop 2 finest known. (No, I didn't pay anywhere close to the price guide).
There’s a third way, besides MS70 moderns, world coins, and chasing an uber high grade US coin: buy something that’s unique, 1 known. If you’re willing to branch out into Civil War tokens, R10 (unique) tokens are out there and much more affordable than regular US coins, if you’re not picky about exactly which one you end up with. That’s probably not what you meant, but it is a path to a top pop, desirable numismatic item that is never going to be eclipsed.
If you are looking for a great representation of the Buffalo Nickel design, here's a coin that I think shows off the design better than most. This is a 1936 Satin Proof in PR-67, CAC. The price is a bit over $2,200 If you wamt a Brllant Proof, this is a PR-67. These will run you over $3,000 If you have a smaller budget, this 1938-D is in an NGC MS-66 old fatty holder. The grading tended to be more conservative back then. This would retail for $60 to $65. None of these coins are finest graded, but there are a couple questions you should consider. First, can you tell the difference between these pieces, and the pieces that are one or two points higher? Second, sometimes the question needs to be asked, is there really a difference or a difference in quality that can justify the the often huge "POP-1" price premium? There is registry collectors out there who will simply pay a high price to get the most registry points, even if the coin is sub-par. Years ago there was a 1963 cent that was graded PR-70, Ultra Cameo and the "finest known." The trouble is it had black spots all over it, and clearly was not a PR-70 any more. That didn't stop some of lemmings from bidding it up to over $40,000! Outside the holder, you would have had a hard time getting $10 for it. Sometimes "POP-1" status can make some collectors go "insane."
Top pops on a budget. Try Variety hunting. My first Cherry Pick was $60, sold for $3,549. Second was $28, sold for $3,500. Repeat that a couple dozen times and you can make top pops yourself. Another option is to infiltrate the registry, cozy up to the top pop set owners, then sucker them out of their top pop duplicates for cheap. I don't advise option 2, but I know a Washington Registry fiend that does just that. Acts like he's everyone's buddy but all he wants is their coins.
This. My only top-pop coin, a Belgium silver 50F in MS66 (population 2), was $45. But it's a common coin in even slightly lower grades. I wouldn't say world coins are more affordable than US coins in general, but reasonably common coins in high grades are.
Coin collecting is about having fun. Know thyself. If your top pop becomes more common, will you be bummed out about the coin? The coin will not have changed (well, hopefully it won't have changed in the slab), yet your perception of it might. If you think this is a reasonable likelihood, spend your money on some other coin that isn't a top pop, but is attractive to your eyes. It's still likely to be attractive to you X years down the line.
My advice is to avoid top pop coins as the coins are subject to sharp price swings as new coins are certified and as grade inflation pushes numerically equivalent competitor coins to higher grades with future resubmissions. Assuming you ignore that advice, it really depends on what you are looking for. Common date? Business strike or Proof? DCAM/UCAM or CAMEO, or non-cameo? Better date? You are probably looking at a minimum of a few grand for a decent coin up to six figures depending on what you want.