I am going to make the assumption that you are doing narrative work as opposed to ENG or documentary work. This being the case you want lavs that are easier to hide. Small lavs that have great sound are on the pricey side. Lavs popular with professionals for narrative work are the Countryman B3 and B6, Sanken COS-11, and Tram TR-50. Yes, you can use "larger" lavs, but they are harder to hide and, being larger, are more prone to noise issues, (rubbing, etc.) Also keep in mind that it does take a bit of skill to properly place a lav.
If you are considering a wireless system the absolute minimum I would recommend is the Sennheiser G3 systems, about $600 each. If you go with a lower priced unit you will be dealing with static, drop-outs, hissing and EM/RF interference to name just some of the potential issues.
Just to put things into perspective, many professionals use Lectrosonics wireless systems. The Lectrosonics 100 series starts at $1,200 up to $2,100 per set and the Lectrosonics 400 series starts at $1,900 all the way up to $3,200 per set without lavs.
So, if you really need a wireless lav, RENT!!!!