I'm confused by your use of 'I' and 'my' early in your post,and then 'we' later on. You've not made it clear how many people are in your party (or whether your budget is per person or for everyone).
However the centrally-located Hotel Majestic offers a basic single room (with shared bathroom) for the three nights, for a total of £73.92
For two people, in a twin-bedded en suite room, the total price is £127.44
3-bed and 4-bed en suite rooms are also available, for total prices of £168.21 and £193.80 respectively.
Those prices are room only. Continental breakfast costs €4. I'm unsure about parking but, even if you had to pay, those prices look attractive.
The Hotel Prime in nearby St Jean de Vedas offers free parking. There are no single rooms. Doubles or twins (en suite) work out at a total of £147.84 for 2 people over three nights.
The Résidence Hotel Le Milos, in Castries, also has free parking. A double-bedded en suite room works out at £170.82 for 2 people over 3 nights.
All of those can be booked here:
http://www.hostelworld.com/
(Don't be put off by the word 'hostel' in that web address; there are hotels and B&Bs listed as well).
If nothing there meets your needs, check the accommodation listings on Montpellier's official tourism website:
http://www.ot-montpel.../en/all-accomodations
Also see TripAdvisor's ranked listings (with price guides) for hotels
http://www.tripadviso...oussillon-Hotels.html
and B&Bs:
http://www.tripadviso...oussillon-Hotels.html
Chris