What's the going rate for a 3 tiered cake? 10", 8", 6". Pretty plain cake covered in buttercream but with 6-8 gumpaste very detailed roses?
The going rate where?
Ennis, Ireland or rural Oklahoma? Central London or Las Vegas? Taiwan or Brisbane, Australia?
I'm in the USA
Pricing varies from city to city baker to baker. I'm sure someone will give you what they charge but that may not be accurate for you. What's your cost of ingredients and supplies? What's your overhead costs (power, building rent insurance water etc) how much do you want to make an hour? All those are different for just about every baker. Once you know what all that cost you then you will know how much to charge. What I have to charge is specific my expenses. You'll have to do the homework on your expenses and costs to know what to charge or risk undercharging which isn't good for the cake business as a whole.
across the states it's somewhere between $3 to $8 a serving plus maybe a little more for the flowers -- i would charge around five bucks per serving give or take that would include this decor and roses --
as far as number of servings i go by the industry standard that Wilton has published as a guide on a page you can google called Wilton wedding cake data chart -- only use the one from that site there are many others out there that look like the Wilton one but the numbers are screwy -- in other words don't get one from Google images --
now there are other charts though -- Wilton has party sized serving chart -- Earlene has a different chart and other countries have different charts -- but rest assured most u.s. bakers use a 1x2x4 inch serving even though it sounds ridiculously small it is actually most adequate