Hi Janne,
Don't think it's something wrong to ask for, I am looking at doing the same thing and I have no idea where my margin sits for at the moment for the future.
Thing is a lot of companies now are seeing through the automated software and price fees and looking to get low as possible. So for a custom CMS I think it would be right or even more.
A company that I worked for tried building their own CMS.. Less to say failed miserably.. Ended up purchasing for 6 team members to Subscription based Salesforce software.. Easily costing them £10,000 a Year..
£10,000 compared to Starting £3,00 for a Custom build CMS, I think I know what I would use in the long run :)
I'll look into it a bit more and if I find anything i'll send it over to you :) x