Hi,
I am willing to do this task. I can change the meta titles of 6000 products with an efficient way. I am already worked with 8-10 Shopify website. So, I gather the knowledge you might be needed for this type of task. I can do this task within 1 day and mu=y budget for 6000 products are $25-$30 USD. If needed, other works also can be done like meta description change, template change (free of cost).