Not all 10 speed is created equal. It's going to depend on what your current model DR's are. Tiagra 4700 is 10 speed, but it has the pull ratios of the 11 speed groups.
Shimano 105 5700 hasn't been new for some time. So you'll only find NOS or used on eBay at more than new prices.
Is your current stuff 105 5700? If so, you might just get Tiagra 4700 and change out your DR's too for less money. And then you'll at least have something that is still made today. Though it's probably time for another version of Tiagra to make a debut.