Join With Parsing From Another Column

How to accomplish a join when the join condition has to be parsed from another column? I need a list of all the exchange part numbers with exchange part pricing, but need the description from the original part number. Example:

Part Number Description Cost
123-456-1 A ROUND THINGIE 5
150-387-1 EXCH - 123-456-1 2

Needed record is
Part number ExchangePart Description Cost
123-456-1 150-387-1 A ROUND THINGIE 2

Something like

SELECT PART# as exchangepart,
case
when substring(descr, 1,4) = 'EXC-' then trim(substring(DESCR, 5, 25))
when substring(descr, 1,3) = 'EXC-' then trim(substring(DESCR, 4, 26))
when substring(descr, 1,6) = 'EXC - ' then trim(substring(DESCR, 7, 23))
when substring(descr, 1,5) = 'EXCH-' then trim(substring(DESCR,6,24))

[Code] .....