SEO audit + optimization for 3 WordPress websites (adult wellness niche)

We run 3 WordPress websites for a massage/wellness business based in Budapest, Hungary. All three are currently indexed but underperforming in organic search (low domain authority, thin backlink profile, multiple technical SEO issues).

We recently received a detailed technical + content audit from an agency and would like independent quotes/opinions to compare pricing and approach before committing.

Scope of work we're looking for quotes on:

Technical SEO audit and fixes (duplicate titles/meta descriptions, duplicate/broken indexed URLs, missing structured data, page speed, HTTP/2, internal linking structure)
On-page optimization for existing pages (titles, meta descriptions, H1s, keyword targeting)
New content creation for underserved languages (Hungarian and French currently have zero dedicated content, despite meaningful search volume)
Link building / backlink acquisition (current referring domains: ~24; competitors average ~68)
Ongoing WordPress maintenance and implementation of the above (we can implement basic fixes ourselves with guidance, but want to know your rates for full implementation too)

What we need from you:

A brief outline of how you'd approach this (audit method, tools used, timeline)
Pricing: one-time project fee vs. monthly retainer options
Examples of similar work (adult/wellness/local service niches preferred but not required)
Whether you're comfortable working with an adult services business (please confirm before bidding)

Budget is flexible depending on approach — please quote based on scope, not a fixed number. We're comparing several proposals before deciding.