Ive made a few. Most recently a transmission line set, but that design was somewhat erm.. aquired. Transmission lines are not an exact science so i somewhat followed in the footsteps of others. There these
http://ourworld.compuserve.com/homepages/cmelhuish/speakers.htm but i fitted the morel mdt30s tweeters instead. I moved the terminal plate to the bottom so the box is not weaked at the back of the throat, and there is full access to the line although stuffing was never needed except behind the driver. Honestly, my speaker cables are fine, im not trying to hide anything.
I got the cones off ebay for about £50 the pair. I had the tweeters, there about £35 each. crossovers were a few pound. just 2nd order, nothing fussy needed with good parts. You can add a zobel to sweeten this cone/tweeter combination a little, but its more choice than necesity. sheet of wood is £30 and the main difficulty in the whole process. You need a cutting list that allows the wood bloke to be close, not exact. any inaccuracy needs to cause sandable overhangs only. If you look at the link, many of the pannels have a common dimension. 155mm. You would start your cutting list buy having him chop lots of 155mm planks to make all the 155mm parts from. thus if he messes up it does not matter. This electronics bundle appears in speakers costing in excess of £1000 but its a £300 project all finished nicely.
I recently picked up a pair of mission tweeters for under £20 that appear in there currant flagship models. something like that would make a great upgrade to some cheaper commercial speakers. Tweeters are 10 a penny as most will physically fit. its the woofers that are in shorter supply if you want replacements.
ebay has a 'speaker components' section. Ofton drivers that appear in reviews pop up.