Buying a call option on a bond can be less expensive than buying the bond itself for several reasons:

1. Lower upfront cost: The premium paid for a call option is typically lower than the principal amount required to buy the bond outright.

2. Leverage: Options offer leverage, allowing investors to control a larger position with a smaller amount of capital.

3. Flexibility: Options give investors the right, but not the obligation, to buy the bond at a specified price (strike price), allowing them to choose whether to exercise the option or let it expire.

4. Risk management: Buying a call option can be a way to hedge against potential price increases in the bond, limiting potential losses.

5. Speculation: Investors may buy call options expecting bond prices to rise, allowing them to profit from potential price movements without fully committing to buying the bond.

Keep in mind that options also involve risks like time decay, volatility, and potential losses if the bond price doesn't move as expected. It's essential to carefully consider these factors before making investment decisions.