Following @jordanm advise I searched high and low for documentation and finally came across something similar at https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/spot_instance_request https://github.com/terraform-aws-modules/terraform-aws-eks/blob/master/docs/spot-instances.md

and found this syntax in a related terraform configuration

spot_price = "1.10"

here is how it looks inside the EKS module:

module "eks" {
  source          = "terraform-aws-modules/eks/aws"
  cluster_name    = local.cluster_name
  cluster_version = var.kube_version
  subnets         = module.vpc.private_subnets
  vpc_id          = module.vpc.vpc_id
  enable_irsa     = true

  tags = {
    Environment = "training"
    GithubRepo  = "terraform-aws-eks"
    GithubOrg   = "terraform-aws-modules"
  }

  worker_groups = [
    
    {
      name                          = "worker-group-bot"
      instance_type                 = var.bot_instance
      disk_size                     = var.bot_disk_size
      additional_userdata           = "echo foo bar"
      additional_security_group_ids = [aws_security_group.worker_group_mgmt_two.id]
      asg_desired_capacity          = var.bot_desired
      asg_max_size                  = var.bot_max

      //      availability_zones = [var.availability_zone]
      //      subnets         = [module.vpc.private_subnets[0]]

      kubelet_extra_args      = "--node-labels=node.kubernetes.io/lifecycle=spot,prefer=bot"

      suspended_processes     = ["AZRebalance"]
      spot_price              = "1.10"

      tags = [
        {
          "key"                 = "k8s.io/cluster-autoscaler/enabled"
          "propagate_at_launch" = "false"
          "value"               = "true"
        },
        {
          "key"                 = "k8s.io/cluster-autoscaler/${local.cluster_name}"
          "propagate_at_launch" = "false"
          "value"               = "true"
        }
      ]
    },
  ]

  workers_additional_policies = ["arn:aws:iam::aws:policy/AutoScalingFullAccess"]
}

If someone knows where the documentation resides please comment.