BuyIs outsource is just another variant of buy?Issues with build - maintenance / bcp (if relevant) / documentation / staff turn over / coding errorsQuoteOriginally posted by: FarhadMy department supports advanced mid-office Excel users pricing optionality embedded in contracts. Historically, options are priced using internally built Xll with a library of dozen well-known formulas. Passing parameters into custom Excel formula like ?=Black_Scholes(price, strike,?) or ?=Black_Sholes_Spread(?? typically does the trick.Among 64-bit Windows migration, need for new functions (like call on call), and a need to pass array formulas to option library (need to embed into Excel cash flow array calls like ?=sum(Black_Scholes(A2:A5, ?)?, I am thinking of upgrading this legacy add-in. I do not work for analytical finance company; hence building such library would require organizational effort and maintaining this library from an organization standpoint (source code, development tools, and analytics-savvy personnel) would be a challenge.Since option formulas and Excel have been around forever, I am hoping maybe there is some reasonably priced external vendor I could buy this Xll from? Second best option, if anyone had experience with external vendor building these dozen or functions Black-Sholes flavored functions in Excel Add-in? There is a price threshold, too: if I could simply charge my corporate card, I would buy such Add-in library. But if I have to pay hundreds of thousands in consulting fees, we?d build this internally. Would appreciate references or experiences.