We all like playing with servers etc, don't get me wrong - i'm no different, but if they are put off the server idea due to the cost, look at a SaaS accountancy solution such as quickbooks or brightpearl, in effect you'll be offloading the hardware and DR side of things to a third party who has the infrastructure/skills to support it properly, while getting a comprehensive LOB application for very little up front cost for your customer.
You'll find a lot of small business' will find this pricing model attractive, they don't have to worry about backups, can access it from home or the office 24/7 - and ultimately sell it to them as a 'solution', something you will manage and support for them as the 'IT Expert', charge them a monthly support and consultancy fee for doing so - this way you retain their business, have a predictable income month on month, and the customer has a comprehensive system with very little upfront costs to pay.
I'm finding a lot of customers, especially really small ones (1-10) are moving over to SaaS based solutions because as for hosting internally
1.) they can't stomach the cost of server, backup apparatus and a UTM.
2.) no one wants the responsibility of swapping the backups out everynight, again additional costs for offsite backups and/or USB drives etc
3.) They do just 'one thing' all the time, and they don't need a full blown SBS or essentials server and all the frilly bits such as exchange, sharepoint, AD DS etc.
and remember for very small offices, setting them up in a 'workgroup' is usually sufficient especially for basic things like sharing files off a small nas and perhaps one office printer. It's all about fitting the solution to the requirements, and being smart/frugal about it - that's how you'll be profitable and make a success from it ultimately.
Just a thought....