It is generally legal to buy property in Usarli Khurd, Panvel, which is an affordable area in Navi Mumbai. However, it's crucial to verify land use (agriculture vs. residential) and obtain all relevant documents. Consult a local advocate to confirm the property's marketability and understand if it will receive Occupancy Certificate (OC) and Completion Certificate (CC) from CIDCO, especially since unauthorised structures on government land are demolished.