Instead of paying 37 Caps or more for Stimpaks, go to Tenpenny Tower. Go to the bar, save the game, hack the terminal, and activate the 50% VIP Discount and 10% Holiday Discount to get everything on the menu for what it is worth. The inventory is:

Beer: 2 Caps
Stimpak: 25 Caps
Vodka: 20 Caps
Whiskey: 10 Caps
Wine: 10 Caps

After doing this, the value of items you sell there also increases. For example, a pack of cigarettes with a value of 10 Caps now has a selling price of 9 Caps.