Challenging indoor shoot

I spent last night working on another assignment from my church. We have a dinner before church every Wednesday night and they wanted some photographs for the website. My challenge was to find a shot that tells the story of Wednesday night dinner on its own, as they will probably only use 1 or 2 of the photographs on the website. The other challenge was the lighting. One half of the dining hall has a huge stained glass wall making for challenging WB conditions but provides enough light at sunset to shoot at 400 ISO. The other half of the hall (where most of the people are) is very dark and 1600 ISO barely pulls the shots out. Even when it does, the noise level is very high. All I have right now is the onboard flash, but even with an external flash I can't see it filling any significant portion of this dining hall. I used my kit lens for this shoot which is f/3.5 on the fast end.
So, what should I do? I can try to get closeups of people with the flash, and see if they can live with the dark background. I can try to only take photographs on the bright side of the dining hall and adjust the white balance in the post processing. I can also try to save up and get the f/1.8 50mm lens that only costs about $75. With the increased speed of this lens I might be able to get the shots on the darker side of the dining hall at a lower ISO. The only problem with that solution is I am not sure it will work. One other idea that I almost forgot about is to shoot these photographs in the second dining hall. I never eat down there, so I forgot they serve dinner in two different places, and the second one has much better lighting.
I am going to get some samples of the ones I took last night to the people requesting them so they can give me some ideas on composition. Hopefully I get the shots they are looking for next week.