FLUWEL only delivers size 12cm circumference tulip bulbs or larger. The flowers produced by small bulbs (10-11cm or 11-12cm) will look small next to flowers from 12cm+ tulips. Why go to all the effort of planting only to spoil the end effect by using smaller bulbs? Your savings will be negligible and much of the time and effort spent planting will seem wasted. Larger tulip bulbs simply produce superior plants with more impressive flowers.
With daffodils, large bulbs will give you 2-3 flower stems in the spring, smaller bulbs just one. The definition of "large" for a daffodil is harder to pin down, because some daffodils naturally make bigger bulbs than others. But given the choice between a 16cm bulb and a 12-14cm bulb, you (or your client) will be happier with the display from the 16cm bulb. The larger bulb appears to be expensive, but it's actually more economical than a small bulb if you count the flowers you get. And isn't the purpose of planting bulbs to enjoy a great spring display with lots of flowers...