Downtown Dinner for a Group
Yup, I hope everyone likes steakhouses. Morton's is in the 1001 McKinney Building. Vic and Anthony's, Strip Steakhouse and Don Shula's Steakhouse are not far. Irma's Mexican is a hike over closer to MinuteMaid Park, but it is good food. Zula's at 705 Main has always been a favorite of mine for a variety of well made fresh dishes. Sambuca is popular also, though loud at times.
705 Main Street, Houston, TX 77002
909 Texas St Ste 106, Houston, TX 77002
Wow, 5:30 dinner?? I know we're in the US, but that us early even here.
That said, you'll have whatever place to yourself. Since you weren't specific on area (DT or nearby & if so which direction) or type of cuisine (or what you personally mean by "mid-priced) here is a best guess on DT & near DT thoughts with some variety:
Gravitas (loving them recently)
(Name??) at Hilton of the Americas - top floor
Huynh or Mai's for Vietnamese
Bistro Jeanette for good Belgian (not sure of hours)
Black Lab is English & a little further, but convivial.
Spaghetti Warehouse (can't believe I'm adding it, but it could be fun for a group - decent Italian)
Hearsay Gastro Lounge
Zelko Bistro (Heights)
912 St Emanuel, Houston, TX 77003
What about something in the Pavilions like Guadalajara del Centro? It's not amazing but the prices are in the range you're looking for, and I was pleasantly surprised by the quality of my meal when I had lunch there recently. It's a four block walk from where you're staying. I've also heard decent things about Andalucia, but can't attest to it from personal experience.
Bombay Pizza Company is also great, but may be too casual for what you're looking for. Perbacco could also work for you (although it's not a huge place, so you may want to call ahead to see if you can reserve for a group your size).
All of the above are more affordable but not very upscale -- none are holes-in-the-wall, but I'm not sure what kind of business dinner this is.
I would consider all of these walkable from your location. Some of the other suggestions provided are great places, but you would need to drive.
A more upscale option than these would be Artista or most of the steakhouses mentioned -- Artista is definitely on the outer bounds of walkable (especially with the weather like it is).
800 Bagby Street, Suite 400, Houston, TX 77002
700 Milam St, Houston, TX 77002