Absolutely! The bell is one of the biggest single factors affecting the tonal palate and response of a horn. There are earlier threads on this forum which discuss this in detail...
To make an extra flare, you have to make an entire new bell piece and discard the tail. So, it is a significant proportion of the price of a new horn, but another way to look at it is that by modifying the sound and response it's like getting a second horn at a fraction of the cost! Base prices for new flares from custom makers are typically around 500 Euro, with garlands, hand-hammering and lacquering all costing extra, so the advertised prices seem quite fair.
I use two bell flares with my Kuehn:
A single-seam hand-hammered bell - incredibly responsive and colourful - for solo, horn ensemble, mixed chamber and orchestra.
A spun bell with garland - very smooth with extra projection - for brass ensemble, wind orchestra, big band and amplified groups.