I also agree with the Lamy 2000 idea. But other pens with flat tops fit in with modern understated looks. If you want something low cost and like your MR you could get a Pilot 78G. Similar nib and can get them cheep on eBay. If you want a gold nib a Pilot Custom 91 in black would get you nice pen with rhodium plated nib and clip. A little larger and more money the Pilot Custom 912 would also fit the bill.
The Sailor ProGear would work.
Like someone said a Parker 45 looks like a lot of Parker ball point pens. It's a vintage model but there are lots of nibs and replacement parts still available and it's a C/C pen.
Most dark colored non-gold trim flat top pens would work. Cigar and pointed shaped pens just scream look at me more. Also anything that looks like a Montblanc would be right out. That is one brand people are programmed to notice as being "expensive". Like wearing a Rolex.