Finding hotels in the field is more difficult than it used to be, with increased business and tourist travel in these areas and especially from May to September. I therefore recommend booking ahead but not yet. The hotels in this region have not yet loaded themselves (and their pricings) in for May yet, so databases on the booking sites will either not have the hotels or will show pricing as "on request." Wait until beginning of April to try.

When ready to book, also check www.sinohotel.com or www.elong.net in addition to ctrip. I use all three with good results.

My Silk Road report (search on this forum for it) has list of hotels I stayed at in each city. I am also in your price range. In general, what you pay for hotels in Xinjiang gets you less than what you'd get for the same money in much of eastern China. And unfortunately in places like Kashgar and Turpan, there are next to no branches of the East China simple and reliable "motel" chains like Home Inn, Jinjiang Inns, etc.