Prep work will determine the final finish. I wouldn't think that just pressure washing parts would be sufficient. If there is any grease or old paint still on the part, the powder won't stick for long. Sandblasting or glass beading is really the best way to prep a part for powder. Otherwise you're just throwing your money away on a coating that won't be any more durable than paint. Think of powder as paint--the requirements for prep are the same--clean, dry and oil free.
As far as ovens, buy a used electric oven at a garage sale or something. You can get them for well under $100. Make sure it's electric. I use the oven racks for hanging my parts, so all I do is transfer the rack to the oven with the part hanging under it, and bake it.
Hope this helps.
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