I disagree heartily about programming it yourself. You can set up a basic Monte Carlo simulation model in Excel in less than 30 minutes. You can easily set it up such that every row in the spreadsheet can be a trial and then drag down 1,000 rows to run 1,000 simulations. IIRC, you can hit F9 to recalc to re-run your 1,000 simulations as often as you want, which gives you an idea of the range of outcomes you might expect.

In my opinion, whenever you are doing Monte Carlo (or any stochastics) you should spend 90% of your time worrying about whether you have your model parameterized properly and only 10% of your time worrying about whether its appearance is elegant or whether you've run enough trials. Your biggest fuck-up is likely to be caused by choosing the wrong mean/standard deviation if those are the two principal parameters that you use. You can fuss and fuss about your model, but it's likely that your choice of parameters will be your most significant failing (ie, you've selected a standard deviation of a security's return based on data from year 2010-2017, but those years no longer reflect reality for the company today). Go ahead and parameterize your model the best you can, and then spend lots of time asking yourself what the impact will be if your parameters are not valid (ie, run it many time with different parameters to get a notion of sensitivity). Then after you've done this, toss your model out the window and just spend your time thinking.

SJ