Premier Inn London St Pancras is at 88 Euston Rd, Kings Cross, London. The price that comes up on their website is $111. per night, right now, but you can research it for July. (You know your exact dates; I don't.)
Another time I looked at their own website, the price quoted was "Price from £77.00".
Phone:+44 871 527 9492
The website says:
"This hotel is a 5 minute walk from King's Cross St Pancras station, and a 7 minute walk from Euston station. The British Library is 2 minutes' walk away. Bright, airy rooms have casual decor with modern furnishings. They come with en suite bathrooms, flat-screen TVs, work desks, and tea and coffeemaking equipment. After an initial free period, WiFi is available at extra charge. The on-site restaurant serves cooked breakfast, as well as classic pub grub and a children's menu throughout the day and evening."
I will tell you, from my experience, this area is served by many bus lines going past it on Euston Road. It is walking distance to the British Museum, south several blocks.
Nearby is the Hilton London Euston--$105.
There was no Ibis at King's Cross St Pancras.
This area would be convenient for sightseeing in London and for leaving on Eurostar to France.