The deployment of mobile LoRa gateways using low-cost single-channel hardware presents a significant challenge in maintaining reliable communication due to the lack of dynamic configuration support. In traditional LoRaWAN networks, Adaptive Data Rate (ADR) mechanisms optimize communication parameters in real time. However, such features are typically supported only by expensive multi-channel gateways. This study proposes a cost-effective and energy-efficient solution by statically selecting the optimal Spreading Factor (SF) using a two-phase algorithm. The method first applies rule-based exclusion to eliminate SFs that violate constraints related to distance, data rate, link margin, and regulatory limits. Remaining candidates are then evaluated using a weighted scoring model incorporating Time-on-Air, energy consumption, data rate, and link robustness. The proposed algorithm was validated through extensive field tests and NS-3 simulations under line-of-sight conditions. Results demonstrate that the selected SF matched the optimal SF in over 92% of cases across 672 simulated scenarios, confirming the algorithm's effectiveness. This approach offers a scalable alternative to dynamic protocols, enabling reliable mobile LoRa deployments in cost-sensitive environments such as agriculture and rural sensing applications.