Upvote:3
There is no set amount. An applicant needs to show that their sponsor has sufficient resources to support the applicant in addition to themselves and any dependant family.
Source: V4.2 https://www.gov.uk/guidance/immigration-rules/immigration-rules-appendix-v-visitor and guidance on maintenance and accommodation provided by a third party in https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1112745/Visit_caseworker_guidance_12.pdf#page24
See also What supporting documents should I include in my UK visa application?