One option is to get Sugino tandem cranks. Well the right crank will be a tandem crank and the left crank will be a normal bike crank. With the tandem combination you avoid the spider on the right-hand crank cause tandems are weird like that. Look at a tandem bike and you'll see that the front right crank does not have a spider.
The Sugino cranks are fairly inexpensive. About $30 for the pair plus shipping and handling. They're in the QBP (Quality Bicycle Products) catalog and any bike shop can order them. The QBP catalog lists the LH and RH cranks separate. Here's an online source: 'Sugino RH crank 170mm' (http://aebike.com/site/page.cfm?PageID=30&SKU=CR8874) 'Sugino LH crank 170mm' (http://aebike.com/site/page.cfm?PageID=30&SKU=CR2038) They're also available in 175mm.
I used the Sugino cranks on my Pashley muni. They're good cranks. Better than Lasco or Dotek. And not overly expensive like Shimano cranks. The Sugino cranks are forged which makes them better than other less expensive cranks.
I have a pair of 170mm bicycle Euros that I used first for the Moonride in New Zealand. They seem fine for light-duty Muni on a Coker. Even though they look thin, they are actually pretty strong (and heavy). I also have used a pair of 165mm Black Widows, and 170mm Ritchey Logic (bike) and 175mm Sugino Tandem cranks that I use sometimes. They all are fine since I am not trying to break Ryan's 7 1/2 foot Coker drop record. Brian probably has the best advice for budget 170mm cranks.
