Since OP starts with trying to limit expenses, I am guessing that various, more upscale properties may not fit the bill. OP doesn't say much about what expectations are for the property. For me, I don't care too much about high end amenities, particularly on a short trip such as OP describes. I would guess that a short trip would be spent out and about, rather than at the spa. If paying with points, I think the MR at Regents Park is a good compromise... close to the tube, lounge, reasonably quiet and not particularly expensive at 40K MR points.