Co-founder & CTO at 3D Printing software company, AstroPrint. Software engineer & Founder Institute graduate. Mobile and SAAS platforms. Former developer evangelist at Nokia. Mobile at Chiill.com.
If you have your CAD design done, you can get it printed in plastic first using inexpensive printers at 3DHubs for example. Do tweaks to the design and reprint. This can't cost more than $5 or so per print.
Once you're happy you can then send your design to shapeways or i.materialise to be printed in metal. These services will likely charge a fee $100 for a metal print.
I'm the CTO of https://3dagogo.com a marketplace of proven to print 3D designs.
We look at the two sides differently. There's not a single customer. In our case you have designers and purchasers ( sometimes the same person can be both ).
Cost and methods for acquiring designers are very different than those to attract purchasers.
I would clearly separate the sides and come up with separate cost structures.
In my opinion when you're looking at the marketplace from the purchaser perspective, the other side's acquisition costs can be seen as fixed marketing costs.
Find a channel that already carries one side and, find out if you can 'borrow' their content or access to people.
For example you can scrape yellow pages listings for car dealerships ( filling up the seller side ) and make posts of thier pages in your site on Craigslist (getting some buyers to know about you). Make sure your listings have top notch SEO built-in and don't worry too much about the little traffic that Google brings initially, it'll grow.
Make it super easy to share the one action that sets you apart with their friends.
All the while start marketing heavily to the sellers side. Do manual, non scalable work here, it doesn't matter at this point. Promise that you'd post to Craigslist for then, run Facebook ads of the pages in your marketplace, etc. Baby this new customers, learn from them, become their friend.
In my experience it's always easier to find 'brave' sellers willing to try something new. If your product is truly differentiated and you provide the necessary social tools and feedback loops, users will slowly find he site, have great experiences and start talking to about them with their friends and one day... You get critical mass and ball stars rolling on its own.
Good luck. Give me a call if you'd like to brainstorm more.
PHP would probably give you the biggest pool of available developers which will help keep the cost down. If you pair that with a modern compiled framework like phalconphp.com and stay with php version 5.5 with its opcode and memory optimizations, you'll be able to run your site in low end ec2 instances for a long time.
I have always used the guidance provided by the Founder Institute. They "open sourced" thier advisor agreement. Don't forget to read the addendum for explanations on % depending on involvement and company stage.
Check it out http://fi.co/contents/206
I wrote a couple of articles when I was going through it for the first time:
I hope you enjoy them. I can talk in length about this as it's still relatively fresh in my mind.
I'm going to talk from the perspective of a founder, not a lawyer. I also live in California and your state laws might defer.
I think if you are putting hours into your startup, you are also an 'employee' in addition to a founder.
Your board (ie. your cofounders) can decide at any time that you are not pulling your weight in the project and don't want you involved. Thus you can also be 'fired'.
In most vesting agreements there's a right to repurchase unvested shares that the company has. This is essentially how vesting works. The company decides that they don't want you anymore and they have the right to repurchase from you all the unvested shares at the price they were given to you initially ( not current market price ). You can only keep the vested portion.
I hope this helps