could not cast numeric (decimal) to formated text

Hi all...

i have a database-table (postgresql) with 3 columns: id (integer), year (integer) and cost_pre_hour (numeric(10,2)).

I would like to use this table as a source for a dropdown.
As choicelabels I want a contaminated string in the format:

‘Price for year ’ + [year] + ‘ (’ + [cost_per_hour] + ‘)’
[cost_per_hour] preferably formatted with 2 decimal places.

I just can't get it to work.

what i tried:
in the record-type another calculated field:

a!customFieldConcat(
{
"Price for  ",
recordType!<recordType>.fields.year,
" (",
?????????
" euro/hour)"
}
)

for ????????? i set:
text(recordType!<recordType>.fields.cost_per_hour,"#.##0,00")
or
cast(typeof(1.0),recordType!<recordType>.fields.cost_per_hour)
or other internal-cast-functions or/and combinations.

I got the error Could not cast from Record Field to .... CastInvalid or something like that

When i try:
tostring(recordType!<recordType>.fields.cost_per_hour)
i see: Price for 2001 (cost_per_hour euro/hour) 
Realy... the name of the field instead the value.


Why could appian convert a numeric(integer)-field to the correct string without problems (field: year) but with a numeric(decimal)-field 
i got an error or the wrong result.
What is the correct/best way to set a combination of record-type-fields (incl. a formated numeric(decimal) field) as choicelabels in an dropdown?