You should be able to use decimal type. Decimal is the backing type for Decimal, Numberic and Money.

Thanks, but i don't get it to work,

        [Searchable]
        [IncludeInDefaultSearch]
        [BackingType(typeof(EPiServer.Commerce.SpecializedProperties.PropertyDecimal))]
        [Display(Name = "ListPrice", Order = 1)]
        public virtual decimal ListPrice { get; set; }

I get

A meta field with the same name as the property 'ListPrice' exists, but has another data type. Property type: ShortString. Meta field type: Money

When i try with string i get

The property 'ListPrice' on content type 'VariationContentBase' is of type 'System.Decimal' that cannot be backed by PropertyString, it only only supports types String.

Trying with float:

A meta field with the same name as the property 'ListPrice' exists, but has another data type. Property type: Float. Meta field type: Money

The error message is quite clear: 

"A meta field with the same name as the property 'ListPrice' exists, but has another data type. Property type: ShortString. Meta field type: Money"

So you created a property with type ShortString before. Two properties can't have same name but different type. You need to delete that one.

Also in this case BackingType is not needed.

okey, but i don't want to delete it, since the property is in use, also there is no delete button available in Old Commerce Manager on metafield.

Remember i trying to make a strongly type product of an existing MetaClass =)

I interpreting the error message as "Hey, you are trying to do this, but there is allready a property of that type"