I’m only seeing a fight on 8/28 and one possibly on 9/1 according to the serviotoro.com website. The Las Ventas website doesn’t list fights that far out. Schedules change more frequently than one would think.
If you’re dead set on seeing a fight and that is the only option, then by all means drive the 40 minutes to Colmenar Viejo. The drive is an easy one. As of 7/9 the cheapest ticket from the website was €50.50. Buying your ticket at the venue is much less expensive.
I will recommend not buying a ticket very far in advance, if at all. I say that because tickets are non refundable and there’s always a possibility of bad weather or you will change your mind. Note below that a printed ticket is required, not digital.
Here are the conditions if buying from the servitoro website for that series of fights:
“The price includes management fees and the promoter’s surcharge.
Seats are not individually numbered at the time of reservation. The best available seats will be allocated on a first-come, first-served basis. All seats in the same order will be together.
To enter the venue, it is essential to present a printed PDF ticket. Entry will not be permitted with an invoice or digital ticket.
Please confirm receipt of the email containing your tickets (check all folders, including spam or junk mail).
A discount of €35 has been applied. Offer valid from 4th of July while stocks last.”
The last fight I went to was in Madrid (2007) and we bought tickets the day of the event from one of a number of kiosks just outside the bullring.