Just for fun I'm going to take a new cut at this. From the top.
To minimize cost, as the title requests:
Build more packs from tool and laptop 18650's salvaged from packs that have gone "bad". They won't last too long but the pricing is very low. Probably as cheap as you can go. Well, maybe not the cheapest, some techniques below might be free or even profitable...
Use Walmart car starting Lipos and wear them out before the warranty is done and get your money back. Maybe even make a small profit. (It's been done).
Buy Lipo on deep sale. By the way, a lipo pack that is lightly cycled and properly managed will last far longer than a few hundred cycles. Don't know where you got that, but it isn't correct. I've gone years with Lipo, charging twice per workday (up tp 50-70% cycle) and it was no problem, the batteries didn't die in a couple hundred cycles.
Buy LiFePO4 on clearance - prices are occasionally fantastic as people move away from them and there is some really great fire sale pricing.
Have wesnewell build your packs for you.
What not to do - buy the latest technology with the highest promised performance - this always costs more.
Also don't put your location in your data so people cannot be as helpful with suggestions about local sources. Either keep it a secret or bury it in the conversation so it gets lost and you miss out on useful feedback.
Think out of the box. Solve the problem in some other way - I solved the problem of wearing out my commute batteries by cutting out the working (and commuting) part. Now my batteries last a lot longer. Work via internet, win the lottery, retire, marry rich, trade stocks and bonds, real estate, etc. Lots of information, seminars, etc on how to do this, must be easy. Move near your work. Get a job close to home.
What really to do - buy a good commodity product that is widely used, generally something that is used for (or built from components for) a much larger market. One example might be 18650 cells like the ones Tesla uses. They have pushed the cost, reliability, safety and performance way out there and the price down. This is where the price/performance is optimized, the research has already been amortized and the best value lies.
In the particular case of the Tesla perhaps used modules are available at even better pricing. Buy a full vehicle pack and sell most of it off at a modest markup so the part you keep is free.
Make ebike batteries and sell them, using the profit to pay for your own batteries, which are then free.
Also - for commercial packs - buy from a reputable distributor that you can get service from. If a pack needs a cell replaced or a BMS you need access to that service, and shipping a lithium battery with known problems can be subject to huge fines. Buy it locally, build it yourself, prepare to deal with that in some way or another, or be prepared to discard a costly pack and re-purchase if something goes wrong.
Treat your batteries properly for longer life. Your experience and expectations for pack service life seem to be very low for some reason. Make the pack large enough that you can live in the 20-80% charge range for "normal use". Store at proper temperature and charge state. Use quality chargers that treat the cells properly. Keep them balanced. Don't charge past 80% often, and when you do, run it down right away. My commute machine eventually got an upgrade to Multistars at 32 amp hours, and the most I would use for a half-commute was about 13 amp hours. They just last and last. Plus if I have to I can make a roundtrip commute without charging. For longer trips I parallel another 8 amp hour booster pack and take it up to an even 40 amp hours at 75 volts hot off the charger. It goes a long way.
Or buy a used Nissan Leaf - get a 24 kWh pack for about the price of the batteries alone. Drive that for awhile, especially in bad weather and see if you still want to ride your ebike anymore. The range is 80 miles or so and it can carry more than my ebike in either passengers or cargo. It is warm and dry inside, the stereo is better and the seats are leather (or something like it). Used electric cars are cheap - not too many folks are buying them so a 40k$ car with a 6k$ battery is selling used for 5-12k$ or so.
I love my ebikes, but the used Leaf SL is really nice too. Tennis team practice is 20 miles each way, it is 40 something degrees out and dark, and the route is 2/3 freeway (yes, this is real). Do I take the ebike? The heated seats are really nice on those tired muscles, especially on the way home. If you set the timer the car will already be warm before you get in, at least for the outbound run.
I hope you enjoyed this. In spite of the humor there's a lot of experienced based data in this posting.
Have a great 2017!