Commercially Available Cables:
Look for reputable brands that offer longer XLR cables at a reasonable price. Brands like Mogami, Canare, and Hosa have options for longer cable runs.
Bulk Cable and Connectors for DIY:
If you're comfortable with DIY, you can purchase bulk XLR cable and connectors to make your own cables. Mogami and Canare also sell bulk cable that is well-regarded in the audio community.
Online Audio Forums: Visit audio enthusiast forums like Gearslutz, AVS Forum, or Reddit's r/audiophile to see what other enthusiasts have used for long cable runs. You can often find recommendations from people who have faced similar situations.
Local Audio Shops: Consult with local audio equipment stores or pro audio shops. They may have cost-effective solutions or be able to provide advice on suitable cables for your specific setup.
Used Cables: Consider checking for used cables from reputable brands in your desired length. Many audio enthusiasts upgrade their cables and sell their previous ones, which can be a budget-friendly option.
When choosing or making your cables, be sure to maintain proper cable management and keep them away from potential sources of interference (power cables, electronic equipment) to ensure the best possible audio quality.