The Nexus 5 has been replaced, sorta. The Nexus 5X isn't exactly as small as its predecessor, but it carries the cheaper Nexus mantle nonetheless. Still, at a starting price of $380, it isn't cheap. That's hardly flagship dollars, sure, but we're not talking budget bucks either.
Though thanks to a seller on eBay, you can get the original Nexus 5 for just $175. Shipping is open to much of the world, though folks in Alaska and Hawaii are out of luck in regards to US buyers. Shipping is free.
The Nexus 5 remains a perfectly usable device. It may be approaching the end of the line in terms of support, but you'll be hard pressed to find a piece of Android hardware with more custom ROM support than this one. Install CyanogenMod. Install Ubuntu Phone. Install Firefox OS if you want to.