How much does used curriculum really save?

I've often wondered on my extremely slow dial up connection how much money I actually save when I spend months scouring Ebay and various For Sale boards looking for what I want in good condition at a reasonable price. This year I decided to keep track. The curriculum list below is for Jessie to use in 4th grade. All of Violet's 2nd grade curriculum will be handed down from when Jessie was in 2nd grade. The list also leaves out any curriculum that I am putting together myself using library resources, any that I haven't decided on yet, and any non-curricular items. I'll update the list periodically as I get in more books or decide to add or delete things from my list. It will be interesting to see by the end of June what the cost savings actually are.


MATH:

1. Singapore Primary Math 4A Textbook ($7.95) USED ($3.00)
2. Singapore Primary Math 4A Workbook ($7.95)
3. Singapore Primary Math 4A Intensive Practice ($7.95)
4. Singapore Primary Math 4B Textbook ($7.95) USED ($3.00)
5. Singapore Primary Math 4B Workbook ($7.95)
6. Singapore Primary Math 4B Intensive Practice ($7.95)
7. Singapore Primary Math 4 Challenging Word Problems ($7.50)

Total cost for math: $55.20
Cost saving so far: $9.90 (18%)

Language Arts:
Spelling:

1. Spelling Workout F NEW ($12.37)
2. Spelling Workout G NEW ($12.37)

Grammar:

1. Rod and Staff, Building with Diligence ($14.90)
   

Writing:

1. Finish Aesop with Core manual only ($0.00)
2. Poetry for Beginners with Core manual only ($31.95) USED ($15.00)
   

Total cost for Language Arts: $71.59
Cost savings for LA: $16.95 (24%)

Latin:

1. Latin for Children Primer A ($21.95)
2. LfC A DVDs ($54.00)
3. LfC A Activity Book ($16.95)
4. LfC A History Reader ($9.75)

Total cost for Latin: $99.95 bundled
Cost savings for Latin: $0.00

History:

1. TruthQuest American History for Young Students 2 ($28.95)
2. TruthQuest American History for Young Students 3 ($28.95)

Total cost for history: $57.90
Cost saving for history: $0.00

Critical Thinking:

1. Building Thinking Skills Level 2 ($29.99)
2. MindBenders A2 ($9.99)
3. MindBenders A3 ($9.99)
4. MindBenders A4 ($9.99)

Total cost for critical thinking: $59.96
Cost savings for critical thinking: $0.00

Total curriculum cost: $344.60
Cost savings so far: $26.85 (8%)