Basic Hilo Id Generator class,

HiloIdGenerator.cs

using System;
using System.Collections.Generic;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Text;

namespace TestEtl.Infrastructure
{
    public interface IIdGenerator
    {
        object GenerateKey(string table);
    }

    public class GuidIdGenerator : IIdGenerator
    {
        public object GenerateKey(string table)
        {
            return Guid.NewGuid();
        }
    }

    public class HiloIdGenerator : IIdGenerator
    {
        private readonly string _connectionName;
        public string TableName { get; set; }
        public string  HiColumn { get; set; }
        public int MaxLow { get; set; }
        public string Where { get; set; }
        private readonly IDictionary<string, TableHilo> _hilos;
        
        public HiloIdGenerator(string connectionName)
        {
            _connectionName = connectionName;
            TableName = "Hilo";
            HiColumn = "NextHiValue";
            MaxLow = 1000;
            Where = "where Entity = '{0}'";
            _hilos = new Dictionary<string, TableHilo>();

        }

        public object GenerateKey(string table)
        {
            if (!_hilos.ContainsKey(table))
            {
                var hilo = new TableHilo {Name = table};
                _hilos.Add(table, hilo);
            }

            var tableHilo = _hilos[table];

            if (!tableHilo.CurrentHi.HasValue || tableHilo.NextId > MaxLow)
            {
                tableHilo.CurrentHi = GetHi(table);
                tableHilo.NextId = 1;
            }

            int id = tableHilo.NextId + (tableHilo.CurrentHi.Value * MaxLow);
            tableHilo.NextId++;

            return id;

        }

        protected virtual int GetHi(string table)
        {
            using (var conn = CreateConnection(_connectionName))
            {
                var cmd = conn.CreateCommand();
                cmd.CommandText = SqlCmdText(table);
                var idParameter = cmd.CreateParameter();
                idParameter.ParameterName = IdParamName();
                idParameter.Direction = ParameterDirection.Output;
                idParameter.DbType = DbType.Int32;
                cmd.Parameters.Add(idParameter);
                conn.Open();
                cmd.ExecuteNonQuery();
                conn.Close();
                return (int)idParameter.Value;
            }
        }

        private string SqlCmdText(string table)
        {
            string where = string.IsNullOrEmpty(Where) 
                ? "" 
                : string.Format(Where, table);
            
            StringBuilder cmd = new StringBuilder();
            cmd.AppendFormat("SELECT {3} = {0} FROM {1} {2};", HiColumn, TableName, where, IdParamName());
            cmd.AppendFormat("\r\nUPDATE {0} SET {1} = {3} + 1 {2};", TableName, HiColumn, where, IdParamName());
            return cmd.ToString();
        }

        protected virtual string IdParamName()
        {
            return "@Id";
        }

        protected virtual IDbConnection CreateConnection(string connectionName)
        {
            return new SqlConnection(ConfigurationManager.ConnectionStrings[connectionName].ConnectionString);
        }

        public class TableHilo
        {
            public string Name { get; set; }
            public int NextId { get; set; }
            public int? CurrentHi { get; set; }
        }
    }
}

simple version of a Hilo Class, feel free to use (its only had minimal testing)