You could do something like this.  Add logic to determine customer price group.  Then register your implementation of IPriceService in container

using EPiServer.Events.ChangeNotification;
using EPiServer.Framework.Cache;
using Mediachase.Commerce;
using Mediachase.Commerce.Catalog;
using Mediachase.Commerce.Engine.Events;
using Mediachase.Commerce.Pricing;
using Mediachase.Commerce.Pricing.Database;
using System;
using System.Collections.Generic;
using System.Linq;

namespace EPiServer.Commerce.Sample.Business
{
    /// <summary>
    /// /
    /// </summary>
    /// <seealso cref="Mediachase.Commerce.Pricing.Database.PriceServiceDatabase" />
    public class PriceGroupPricingProvider : PriceServiceDatabase
    {
        public PriceGroupPricingProvider(ICatalogSystem catalogSystem,
            IChangeNotificationManager changeManager,
            ISynchronizedObjectInstanceCache objectInstanceCache,
            CatalogKeyEventBroadcaster broadcaster,
            IApplicationContext applicationContext,
            EntryIdentityResolver identityResolver) : base(catalogSystem, changeManager, objectInstanceCache, broadcaster, applicationContext, identityResolver) { }

        public IPriceValue GetDefaultPrice(MarketId market, DateTime validOn, CatalogKey catalogKey, Currency currency)
        {
            var myPricingGroup = CustomerPricing.AllCustomers;
            if (true)//enter logic here to get customer price group
            {
                myPricingGroup = new CustomerPricing (CustomerPricing.PriceType.PriceGroup, "mycode");
            }
            PriceFilter filter = new PriceFilter()
            {
                Quantity = 0,
                Currencies = new Currency[] { currency },
                CustomerPricing = new CustomerPricing[] { myPricingGroup }
            };

            return GetPrices(market, validOn, catalogKey, filter).SingleOrDefault();
        }


        public IEnumerable<IPriceValue> GetPrices(MarketId market, DateTime validOn, CatalogKey catalogKey, PriceFilter filter)
        {
            var myPricingGroup = CustomerPricing.AllCustomers;
            if (true)//enter logic here to get customer price group
            {
                myPricingGroup = new CustomerPricing(CustomerPricing.PriceType.PriceGroup, "mycode");
            }
            filter.CustomerPricing = new CustomerPricing[] { myPricingGroup };
            return base.GetPrices(market, validOn, catalogKey, filter);
        }


        public IEnumerable<IPriceValue> GetPrices(MarketId market, DateTime validOn, IEnumerable<CatalogKey> catalogKeys, PriceFilter filter)
        {
            var myPricingGroup = CustomerPricing.AllCustomers;
            if (true)//enter logic here to get customer price group
            {
                myPricingGroup = new CustomerPricing(CustomerPricing.PriceType.PriceGroup, "mycode");
            }
            filter.CustomerPricing = new CustomerPricing[] { myPricingGroup };
            return base.GetPrices(market, validOn, catalogKeys, filter);
        }


        public IEnumerable<IPriceValue> GetPrices(MarketId market, DateTime validOn, IEnumerable<CatalogKeyAndQuantity> catalogKeysAndQuantities, PriceFilter filter)
        {
            var myPricingGroup = CustomerPricing.AllCustomers;
            if (true)//enter logic here to get customer price group
            {
                myPricingGroup = new CustomerPricing(CustomerPricing.PriceType.PriceGroup, "mycode");
            }
            filter.CustomerPricing = new CustomerPricing[] { myPricingGroup };
            return base.GetPrices(market, validOn, catalogKeysAndQuantities, filter);
        }
    }
        
}

Hi Mark!

This look really good. And this will work even when the workflow kicks in? I solved it by implementing my own workflows but maybe this is better?

/Kristoffer

Yes the workflow calls the following 

GetPrices(lineItem.Parent.Parent.MarketId, FrameworkContext.Current.CurrentDateTime, new CatalogKey(entry), priceFilter)