The OP asked about portrait lenses. We all know the 85/2.0 is a magical lanes. The 100/2.0 is fantastic and the 100/2.8 is beautiful as well. But these babies are getting expensive.
So I offer the 75-150/4.0 zoom as a bridge. This lens also has got some bad talk over the years but I own 3 and they are great lenses.
Some careful shopping will get you a very clean 75-150 for less than $50 usd, My last 2 were $15 and $29.
Yes,it is 1 stop slower than the 100/2,8 but it's a constant f/4.0 and it's also constant focus, meaning you can change the zoom setting and maintain your focus. This is very handy as you can zoom in on your subject and snap another shot very easily.
So before you dismiss the 75-50 out of hand, give it a try and shock yourself.
Oh, and it is important to always use the built-in lens shade when out in sunlight with this lens.