The most I've spent on a single coin is $1450 for a $10 Lib '02-S PCGS MS64. I also picked up a $10 Ind '26 PCGS MS64 for $1400 at the same show . The next closest would be $500 for a $20 St Guadens '14-S PCGS MS64. I bought it years ago before gold went up. Those are my gold purchases and the most I've paid for single coins. As for silver coins I bought a really nice '43-S PCGS MS66 Walker off teletrade for $475 and a nice '57 Proof Franklin PCGS PR68CAM at a show for $465. I also bought a great 1904-O Morgan PCGS MS66 for $300 off ebay.
I've had a few nice ones, but in the back of my head I know that coins aren't much of an investment vehicle, so the money ends up elsewhere..... Even though they bring the most joy. Haven't yet broken the $1k mark, but my top 3, which are currently locked up at the bank, are: $770 - 1893 $10 Gold $540 - 1876 20 Cent $485 - 1811/0 Bust Half
I believe $130 for a 1909-S Lincoln. Don't have the budget for the REALLY big ones yet. Maybe when the kids finally move out...
I think the best way to look at coins is not as an investment. If you do it'll be like day trading stocks or something which takes all the fun out of it. Collect what you like and the best you can afford. Do your homework so you don't get taken. If you follow that practice and don't try to flip coins you'll do fine. With patience and time your collection will be better and when it does come time to sell, in most cases, you will have made a nice profit or at least more than just throwing that money into a money market or savings account for 20 years.