Looking for practical linear grinding/finishing tool for non-production use

Q. Hi, this is my second question posted to this forum. Thanks for all the help as I'm quite new to the finishing process. I'm doing a railing project out of 316L stainless, using all square and rectangular tubing, with some areas with 2'x2' sheets. This project is a one-off and I don't plan to do this professionally. My question is, I'm hoping to find a linear grinding/finishing tool that will suffice for getting a decent #4 finish that won't break the bank. I'm aware of various systems that I can purchase, but these are all pro quality meant for long and heavy use. I just need to get through this job. Is there a less expensive or "hobby" option for this kind of tool that will also make a decent finish?

I've been using a 4.5" angle grinder and abrasive discs, but I'd like something that gives a more uniform finish on flat surfaces, and which will take less time -- my hands are giving out.

Thanks again!