Does it include a frequency meter?.
As you have the core, the manufacturers datasheet will probably tell you winding details?. For the frequency you mentioned expect a LOT of turns, which is why I suggested winding 100 and measuring.
You specified 100KHz, this is a very low RF frequnency, not a high one at all - I don't see yopu reasoning for not buying one?.
Like I mentioned before, there are various options, depending what you have available - but, for a start, what is it for? - you keep mentioning 'high' frequency, then specifying a 'low' frequency. So tell us EXACTLY what you're trying to do!.