California parents are shelling out nearly $175 for a basic bundle of back-to-school supplies this year as the cost of classroom essentials piles on to already strained household budgets. The average basket of 21 essential school supplies costs $173.45, a 7.7% increase from last year, according to an analysis by Groundwork Collaborative and The Century Foundation cited by Times of San Diego. Some individual items have risen by more than 20%. Notebooks cost about 23% more than last year, while notebook paper is up 20% and index cards have climbed 22.2%. Lunch boxes have risen nearly 27%, while dry-erase markers…