You can have a lot of fun with a 60 gallon Lowe's/Kobalt compressor and a 100 lb pressure pot. I use mine all the time for small projects. Clearly its nowhere near optimum for a full time production environment, but we probably average an hour of sandblasting per week and it does just fine. (You can do a LOT of blasting in 1 hour) Most of the time is spent in the setup, and clean-up. So, IMO, its safe to say its a great starter system.
We did 20 brick pavers a few days ago and this configuration had no problem keeping up. Everybody has to start somewhere. I'm very hands on and would rather have in-house entry level tools versus outsourcing. It gives you the luxury of getting creative and experimenting with scrap HDU, wood, and bricks. Plus, like most folks, you'll find that you can make good daily use of that compressor for grinders and other pneumatic tools, as well as clearing dust off projects before paint. For those reasons, I bought my Kobalt compressor. Then added the pressure pot later to start playing with sandblasting. (Yes, dry air is a must. But its not too big an issue if you blast only an hour or two a week. I drain my tank before any sandblasting, and have both a desiccant filter and a coalescing filter inline to trap the moisture)
For anyone dead set on outsourcing, I'd investigate local CNC shops as an alternative to sandblasting. Sandblasting requires a talented/experienced hand to ensure a consistent depth and pattern across your substrate. CNC requires vectoring software and skills to build the project with your computer. But once you are happy with your rendering, you can have peace of mind that you'll get very consistent results, even with entry level CNC operators. And, the best part is that your electronic copy of that pattern can be utilized for years to come. Just edit the text and you can produce a whole new sign for another client.
With all that said, I feel sandblasting signs is virtually an obsolete practice. But having a small system in-house, the 100 lb pressure pot, along with a couple decent filters, you'll find plenty of "other" projects to justify the cost, and have the luxury of blasting the occasional sign when necessary.
For me, the decision ultimately lies with whether or not you have space for a dedicated area to do your blasting. Partition a small area to keep your sand and dust isolated from the rest of your production area. An entirely separate room, or outside is far better. If having the dedicated work space is an issue, then I'll throw my hat into the outsourcing ring as well.
