Help Needed

I am looking at using zoho for my small business. It is just me. I do about 15-20 invoices a month and have about 50-100 or so clients. If I just use the free account, how fast will I eat up that space and size restrictions? I don't know much about all of that. I don't want to end up having to pay $25/mnth when there are cheaper options out there so I don't want to start using zoho if I quickly run out of space.