When you are in dialogue with a musician, it is important to be transparent on both sides about what equipment you can offer and what equipment the musician will need to have.
Many Low-Fi concerts are done completely unplugged, and it can make for a magical moment for both the musician and the audience.
If additional equipment is needed, it is up to the musician to be in charge of what they need, but if you would like to help the artist coordinate their equipment and instruments, you can look to the following resources:
Be My Concert's musician and host Facebook page: As a community, other members are often very happy to let you rent or borrow certain equipment or instruments.
Rental services: With a search, you can find several rental services in your area. For example, in Denmark and Scandinavia there are companies like Soundforce that will let you rent sound equipment.