I have been to Jaisalmer 3 times i have always stayed at RTDC hotels they have AC rooms also but not at dunes ofcourse (SAM Dhani) and also they have tents there ,from hotel in Jaisalmer they leave for dunes at 4 Pm every day i don't remember how much they charge for dunes i think 500 - 600 Per person but that includes a 1-2 Km camel ride then some folk programs by singers ,evening tea snacks and finally dinner .
Then people have the option to stay in tents ,also they have permanent rooms at dunes or come back and stay in there hotel back at Jaisal -mer basically its a good option as by paying for one day one can stay in AC room in jaisal mer at day time and also stay in dunes at night .
While going to Jaisal mer i have not done the trip in one go once i went from udaipur as i had to see Udaipur also it took me 8 hours to do Udai pur - Jaisalmer , the other time i had a Tyre puncture in village 2 hours after Jodhpur which took 3 hours to fix as they punture wala was not sure how to open an alloy . He basically had expertise in jeep and trucks
But while coming back this time it took me 11 Hours to from dunes to straight at my house in Delhi which included one hours lunch some where in a jungle before bikaner , and also tea break in evening , so the route was basically JAISALMER -- BIKANER -- JAIPUR - DElHI , I usually drove at 120 -140 KM PH but in between when i saw open roads which were in plenty i went above reasonable speed also .
As said by you 14 hours is a very very reasonable time to reach if one doesn't get a traffic jam in the way , The road were so good at some places like Jaisalmer - Bikaner that its the only road i felt That those who own super cars should live here and not in Delhi , If i ever have my hands on one like Ferrari or Lamborghini i would run to that place ( even though its a dream only but yes BMW 3 -5 series looks like a real in a few years and that is the place where i will Run To) Speed of 250 is quite possible and you can see 5-10 Km of road in in front of you .
Also Don't be conned by some restaurants from Jodhpur to Jaisal mer as the are basically opened to rob Foreigners only they gave us 4 double omelette's for 800 rs and then refused to give 8 pieces of bread for which i again paid 25 rs per slice

(Shame on them ) Indians were stopping at that restaurant but not eating and foreigners were being fooled , and i came to know only after i got the omelette's , Some people are good also one restaurant owner had a price of 300 rs per bowl of veg dish but he told us in Hindi that we will charge you 50 % only This price on menu is for foreigners only and chapati for us was 20 Rs

while for them its was 100
Also in Jaisalmer there is a Small market where there one restaurant ( Kebab Corner )in left corner of that square They serves very good Mutton Kebabs If you re not veg do not miss that it would be best Non -Veg food that city can Offer
Buy diesel at Jodhpur only as after that Pertol pums are there but easy to miss and also qualtiy issues
And Drive Safe Happy Journey