I'm not sure it will be worth it to upgrade any Claris-level bike to 105/Ultegra components from a cost-benefit perspective, unless you went with the older 10-speed versions, because you can't simply swap out a Claris component for 105/Ultegra piecemeal. After several thousand miles, you'll know a lot more about what you want, though I would bet that you'll add a complete bike (N+1) and leave whichever one you buy now as a backup.
FWIW, find a corporate discount code and create an account on Raleigh/Diamondback to see better prices. A 105-equipped
Merit 3 is currently $1,010 with much better components than the Merit 2. In the past (which is no guarantee for the future), they've discounted Merit 3s down to $800. A slightly "better" (from a weight perspective, by my guess)
Diamondback Century 3 is currently $1,050. A little bit over your current budget, but likely a lot cheaper than fully replacing the Claris groupset later.