Watch craigslist and ebay, setup a commercial account at lowes or home depot (you get 10% off) and then build your whole setup. I preffer my truck mounted setup over a trailer because it's alot easier to manuver but a trailer will work just as good if you don't have a 1-ton.
I found a warren rupp 1.5" teflon pump for $125 on ebay and it was close enough to pick up so no s/h. I found a IR compressor on craigslist for $300.
All the plumbing cost a little under $200 (2" black pipe, suction hose, connectors, etc...) I bought my wand from sealmaster for $100, Had the hose made at a hydraulic company for $96 (it's just high pressure hose, not hydraulic hose, and has hydraulic ends on it), I had my tank and strainer, bought it used 3 years ago for $800.
I just built the spray unit this past week and haven't used it yet, so who knows how good it will work
but It looks very proffesional and cost alot less than buying a new setup.