I'm looking for something containing similar functions to Matlab’s financial and financial derivatives toolbox but don’t have the cash to spend on matlab. I would appreciate any info on free or open source libraries or programs that will let me easily calculate interest rates, risk etc.
How about the Octave financial functions?
http://www.gnu.org/software/octave/doc/interpreter/Financial-Functions.html#Financial-Functions
I'm not familiar with the Matlab toolbox, so you'll have to judge for yourself.
GNU Octave is a high-level language, primarily intended for numerical computations. It provides a convenient command line interface for solving linear and nonlinear problems numerically, and for performing other numerical experiments using a language that is mostly compatible with Matlab. It may also be used as a batch-oriented language.
Exactly what functions do you need? How advanced? You have some financial functions in .Net
Im sure it doesnt cover everything, but calulating interests and some other are no problem:
http://msdn.microsoft.com/en-us/library/daksysx3(VS.80).aspx
Calculate depreciation. DDB, SLN, SYD
Calculate future value. FV
Calculate interest rate. Rate
Calculate internal rate of return. IRR, MIRR
Calculate number of periods. NPer
Calculate payments. IPmt, Pmt, PPmt
Calculate present value. NPV, PV