A lot of estimating software has a CSV backend to it, creating something in a spreadsheet like program will work and if "you" were to do it yourself, it would be specifically tailored for you. Depending on how fancy you get with it, could have a nice GUI, but it's still essentially a CSV backend.
Now, this is just for the estimating/quoting end of things. Coming up with one's own estimating/quoting solution is more time consuming then it is difficult.
If you are wanting more then that, could be looking at a CRM solution.
Some hosting companies have solutions that have modules to run it through your website, some are paid for, some are free. Some are even Open Source (sometimes that's free, sometimes it's not, open source doesn't in of itself mean free).
There are some total CRM packages that are self hosting as well that would be cloud based, just on your cloud and not someone else's. This option requires more knowledge from the user, so may not be what you are looking for, but it is an option. Again, paid and free, closed and open source versions of that.
I'm not going to deny that I'm not biased to open source, I like the ability to scale as I see fit, not when someone else does. However, this is totally going to depend on what your needs and abilities are. It isn't for everyone.
I do believe some type of solution is better then nothing, regardless of the level of business, just the solution should be on the same level that the business is at. Don't necessarily go totally high on the hog when the business isn't at a level to sustain that. Some CRM solutions are very cost prohibitive, especially the cloud based ones (which doesn't make sense to me, but I digress) that are closed sourced and subscription.