1. You said that 'it was told to me that for 9 years they will lease my unit at market price',
2. Was it just tole or you had executed and registered an agreement having the above clause,
3. If it is that 'they had told you' the above without any witness and no specific agreement in this regard was executed, then just forget the matter since you shall have to prove your allegation with evidence,
4. If it was a verbal assurance without any witness, then do not unneceassarily burn money in filing case which you can not win,
5. If you have an agreement to thgat effect, then file a specific performance suit agsint the builder immediately.