I have a Stratix here doing NAT conversions. I did not set it up but its been running here for some time now. I only mention it to make the point that I think you can do this with most decent Ethernet Switches. We have large 48 port Cisco switches here that do some NAT routing on the office side.
I had a salesman here once back in the day talking about the capabilities of his switches including the NAT translations. He sells the Phoenix Contact brand.
Id probably look for alternative as well if I was spending my own $$ on this stuff. I usually use the 1783-NATR but even they exceed a cool grand to purchase one. I use one on every project so I bet it would scare the folks here to know what they spend on these each year...