my worksman is solid as a rock. absolutely the best rims+spokes iv'e ever seen on a bicycle.
they are a bit of work but in new york theres worksman trikes that were made into hotdog stands from the 60's still operational, tells ya something about the quality right? really nice steel frames. since you got $800 saved pick up the front drum break for another $90.
pair it up with a sprocket adapter from either manic mechanic, or sportscarpat when he starts selling his version (if you use pat's you wont have to bend a coaster break arm since his bolts are countersunk, and with both of them you wont have to grind down your dustcap which is nice), regardless i'd say avoid the kit sprockets on a worksman cause kit bolts are too short for such beefy spokes, you'll spend $10 or so just on longer bolts (sprockets+adapter made for that specific hub are like $70 shipped), and the rag joints are hard to install just right.
i have a grubee GT-5 and i didnt get to ride much but it felt real nice, everyone says the grubee GT-4 starfires are better though (i think thats the 66cc starfire, not sure what a 48cc version is named), motor kit is like $180 shipped i think, although that was a GT-5, idk about the GT-4 but i think it would be similar.
so $180 for the motor my bike was $50 shipping and a base model with fenders is $329, 90 for the front drum break so $419+50+180= $649+sprocket adapter is like 70 so $719ish, could even maybe pick up an expansion chamber with what you had left, and that would be a really nice bike
the bike does need a few mods though, mainly cut off 1 chain guard mount on the seat tube (i did this with a dremel), and washers between the hub and drop outs to get more clearance. dust cap mod and bend the break arm out a bit if you use a rag joint (which i wouldn't recommend, mine was a nightmare), and i had to move the rear wheel a bit more towards the right of the axle for extra clearance, would be easier with a good chain tensioner, but i didn't want to use one because again, headaches.
good luck choosing a build
edit: also regardless of what bike you pick, if it has fenders scrap the front. http://www.google.com/cse?cx=partner...ycling.com/f3/
and if mountain bikes are your thing you could do a jack shaft, just get a bike with a horizontal frame, so you'll have enough clearance for a motor. jackshafts move your chain drive from the left of the bike to the right side and the through your traditional pedaling set up (meaning if you have a multi gear bike you've essentially created a transmission and have a wide array of gears to use for various applications more speed, climbing hills, a mix of both etc.)