There's a couple guys on eBay selling that booster pump at a good price. Either way you're going to need it so just order it from someone and get some water pumping!
I myself am in a different situation and have to deal with chloramines and high pH (9.5ish) probably from sodium hydroxide which turns out to be about the worst conditions you could have for an RO/DI system.
I've been getting some really good feedback from jdieck on my setup which I believe is going to look like this:
Pressure gauge installed here
1 micron gradient sediment filter SF-MT-1-10
0.5 micron sediment filter SF-MT-0.5-10
0.5 carbon block filter CF-0.5-10
Pressure booster pump Aquatech 8800
Pressure gauge installed here
Two high rejection membranes in series MEM-S-0090 (about 180 gpd)
Strong Acid Cation DI cartridge DI-SAC-CI-10 (This will remove metals and lower the PH of the water to improve removal in subsequent stages)
Strong Base Anion DI cartridge DI-SF-CI-10 will remove contaminants that will exhaust the high quality cartridges in the following stages and bring the PH back to normal level.
Ammonia Removal cartridge DI-AR-CI-10
Mixed bed cartridge DI-SB-10
Pressure gauge installed here
Depending on the "crud factor" of the 1 micron sediment filter I might put a 5 micron in front of it.
But it doesn't seem like you have any of the issues I do so maybe for you to just increase productivity:
5 micron sediment filter
1 micron gradient filter
0.5 micron sediment filter
0.5 carbon block filter
Pressure booster pump Aquatech 8800
2 Membranes in series
2 Mixed Bed DI Resins in series or parallel depending on how you want to run them.
That should make great use of your 6 canisters. It will reduce your waist water by about half (running in series) and increase your production to about 150/180 gpd or equiv.
If your 1st sediment filter cruds up you can always put a cheap 10 micron in front of it but I doubt you'll need it.
Carlo