In order to keep your costs down I would suggest drawing up a thorough plan such as what type of bridge or other parts that may affect the construction as well as materials and tools.
Then, make a list of all your tools, parts & finishing supplies needed for your plan and start shopping.
See what you can beg or borrow.
Find a local wood supplier & maybe a local voc/tech school with shop tools that you may use.
Befriend people with tools and materials...having cold beer or doughnuts at the ready can go a long ways. It helped me! So did talking about hunting, fishing, motorcycles & guitars.
Be prepared to drop an easy $500 on just parts, wood & finishing supplies for medium grade parts.
Brian @ UniversalJems is a good place to find reasonably priced parts, IMO.
Not to mention you'll be supporting this site since it's his.
Good luck and RAWK ON!!!
btw...I'm a noob so take my advice with a grain of salt.