I replaced my MA4-5 p/n 10-1478-1 (O-360) with an Avstar rebuilt about 350 hours ago and it works fine. I actually wanted a genuine Marvel rebuilt but ordered this one accidentally. Marvel Schebler introduced a composite ("Smurf") blue float years ago and I put one in the last carb. It is a huge improvement over the metal floats. I called Avstar and they said they use their own metal float and that it won't fail either. So far, so good...
As for new carbs, we put a new Avstar carb on a Cardinal where I work and the whole thing was machined, not cast. A real work of art. How good it works, well, we'll see.
A new 10-3878-1 carb from M-S looks to be about $3,100. Of course, rebuilt or overhauled carbs are a lot less. An Airflow Performance fuel injection kit is about $3,700 (plus high pressure pump/filter assy). If you wanted a new carb, a conversion to FI might make sense. These prices are for 180 Lycomings, the 160 (MA4-SPA I think) might be lower.
I'm sorry if I just complicated things for you but I hope the info helps...