For a good value comparison, I would suggest looking at PRLX (a METHA competitor). PRLX is trading at a slightly higher price to sales ratio, however they are losing lots of money, they have a lower price/cash ratio, a somewhat higher price/debt ratio, and FWIW, METHV still has 4 million in sales a quarter in what they classify as 'optical' - and those sales just turned profitable last quarter. On a direct comparison to PRLX (of course buying one stock based on anothers price is not always prudent) METHV deserves a considerable premium - perhaps 2/3 of sales vs. PRLX's 1/2.
That gives me a $6.25 a share target - which could be adjusted much higer if they can actually turn things around.
On the downside, if METHV comes near their estimates on revenue and earnings which they just reitterated Friday, I can't see it trading lower than 1/3 of revenues, or about $3+, in most any market.
Having said that, I bought at 3.70, 3.85, 4.01, and 4.12 so I'm biased.