9-10 inch if buy outside.... $40 i think won't be so simple
sponge cake with strawberry cream bah..... $20++ at this cake shop
at holland V can get hazelnut chocolate cake... like cream like
that, with a crunchy base. damn shiok. i had it for my birthday
last year 
and it has white and dark chocolate
shavings on top...
if you want it to be 40 you need more decorations and perhaps
customisation, like writing words on it, or pictures on it. because
this is homemade so its labour intensive, if you compete with those
outside you'll be on the losing end as they churn out a lot for a
low price. so you have to compete based on customisation and
service 
unless your mum has a BIG cake making machine. then i nothing to
say, lol.
