how do i optimize google business profile without a big budget?

Most of it costs nothing but time. Get the primary category right first - it does more than anything else on the profile, and a lot of businesses sit in one that is close but not quite what they do. Then fill every field that applies: services, hours including holiday hours, service area, a proper description written for people rather than keywords. Photos of the real premises and real jobs, not stock. Reviews are the part that needs a habit - ask every happy customer, send them the direct review link so it is one tap, and reply to all of them, the bad ones calmly. Don't stuff keywords into the business name. It looks tempting and it is the quickest way to get the profile suspended.