Just to re-iterate that commuting in Beijing is insane. Even staying in zhongguancun, it will take you more than 30 minutes in rush hour to get to tsinghua.

Unfortunately, the nice hotel options (e.g. Wenjin) near Tsinghua are ridiculously overpriced. If you want to accumulate points, the holiday inn in Haidian is actually very nice, but you'd have to get a cab every day and it may stretch your budget. Depending on what side of Tsinghua your convention is, the Runzejiaye hotel is near the northeast gate, is OK, and usually moderately priced.

There are no options under $70/night in wudaokou that I actually like.

Tsinghua has a couple of hotels on campus: Jiasuo is actually very nice. Jinchunyuan is basic, but OK, and nicely located. But they actually often cost more than $70/night, crazy as that seems.

Good luck!

tb

PS unless you opt to stay in or extremely near campus, I doubt you will make it to your convention in under 30 minutes, no matter where you stay. The nearest subway stops to Tsinghua are all at least a 10-15 minute walk to the university gates, and your meeting may well be another 15-30 minute walk further into the campus.