Everyone wants boots and everyone wants them as cheap as possible. Sure, the cheapest way to get them is through events, but sometimes you are willing to pay for them with gold. Before you go and just click that button to purchase a 7 day boost, consider looking at coffers. They can save you lots of gold. For boosts specifically, you can save 25%-33% by buying a coffer as compared than individual boosts.

Standard Coffer Large Coffer Huge Coffer
Cost $5,160 Cost $13,340 Cost $41,840
Indiv Cost $6,880 Indiv Cost $16,675 Indiv Cost $52,300
Savings -$1,720 -33% Savings -$3,335 -25% Savings -$10,460 -25%
Boost Gold/H Actual Cost Number of hours
Huge Coffer 107.84 41840 388
15Day Boost 115.27 41500 360
7Day boost 119.05 20000 168
3Day boost 120.14 8650 72
1Day boost 131.25 3150 24
15h boost 140.00 2100 15
Large coffer 140.42 13340 95
8h boost 162.50 1300 8
Standard coffer 174.92 5160 29.5
3h speedup 221.67 665 3
1h speedup 340 340 1

As you can see, the best value for the gold you spend is the Huge coffer, by far. It offers the best gold/hour cost and it also provides some smaller speedups that you can use for other things. My approach to using gold to buy speedups and using them is this: I use 7day, 3day, 1 day speedups for research and construction. 15h speedups are good for training t3 troops, 8h boost for t2 troops and 3h and 1h for t1 troops. I have 12 manors and 2 barracks and 1 infirmary. I only buy huge coffers with gold.