If you didn't know, you can book tables at the tents at Oktoberfest which is a good idea unless you want to spend all day standing up. Saying this, finding an open seat during the day isn't so bad but it is at night when tables are almost impossible to find. Price-wise, be sure you have a large group with you (at least 10 people) for Oktoberfest because table reservations cost around 280 Euros.
280 euros per table is about right. Each table seats 10 people so you would be splitting the costs. Also, it doesn't matter if you have less than 10 people, you will have to reserve and pay for the entire table. Do send your booking request by January- February as they start allotting tables in March. If you wait much longer than that you run the risk of the tent reservations being fully booked.
You don't really need table reservation during the week if you get to the beer tents by 12pm-1pm. On the weekend, be there as early as possible in the morning and you won't have an issue of finding a table. By the way, you can also check out the tent’s open-air beer garden; the beer gardens don’t take reservations so you might be able to find a table there.