help! hd, low light, good battery life <$300

+1

Yes if you want good low light capabilities and the cheapest price possible, the refurbished M400 does sound like your best bet. In other words +2

The main reason, besides the price, the HF M400 is being recommended is that last year Canon started putting their HD CMOS Pro sensor in the their consumer camcorders. This sensor is in their professional camcorders, as well as the HF M400.

http://www.usa.canon.com/cusa/consumer/standard_display/hd_cmos_pro

The main benefit is the excellent low light ability. The HF M400 model is also the closest to the your $300 budget. The Canon HFM40 is the same camcorder, but with 16GB built-in storage ($349 at that same Canon site) and the HFM41 is the same with 32GB internal storage and a viewfinder ($399). The HFM400 only shoots to SDHC or SDXC cards - although all three models have dual card slots which will continue recording from one card to another. This is unique to last year's models as this year's (the HF5xx series) only have one card slot.

Good SDHC cards are very cheap now; this camcorder will use Class 4, Class 6 or Class 10 which will all shoot video at the same quality. Two 16gb cards (about an hour and 20 minutes each at highest quality) is a good choice..or if you want to get 32GB cards. SDXC cards are newer and are more expensive.

Another great thing about this camcorder is the Dynamic Image Stabilization; when you hold it hand-held the video will look like a steady-cam.

Although the price is $329, there will be tax and you really should get an extra battery. The batteries that come with camcorders are starter batteries/a spare is recommended anyway. Canon makes long-life batteries; the BP-819 (4 hours on one charge) and BP-827 (6 1/2 hours on one charge; although the BP-827 will make the camera feel heavier). It's a good idea to get genuine Canon batteries, but there are also many cheap generic options - research this well as some cheap batteries on ebay are risky. There is info on this board about them.

The Canon R30/R300 are low line camcorders that don't have this pro sensor - the video quality will be poorer; although it's probably decent in good light - but not "low light" situations as you mentioned in your OP.

You may want to consider things like a tripod, case and a UV protector filter. UV protector filters are screwed onto the camcorders "filter thread" and are clear glass that will provide an extra layer of protection for your lens - this will prevent dust, scratches or an impact to the actual lens. Plus, you rarely have to clean the lens...but if you do clean the lens or filter always use a "micro-fiber cloth" made for camera lens as things like a piece of a shirt or a tissue will scratch the lens or filter. Use a micro fiber cloth to clean the LCD screen, also. The HF M400 has a filter size of 43mm. If something happens to the filter, they are less than $10 versus having to replace a damaged lens.

I don't know the compatibility regarding Linux; I'm sure you can find out on a Linux forum, here and/or searches. As for hard drives, you always want to put your video in more the one spot/back up to a second hard drive. These HD files take up a lot of space. An hour and 20 minutes at the highest quality, (which is recommended to shoot at), will be 16 gigabytes. The good news is that external hard drives are now cheap. You may want to check out sales next week/Black Friday.

The Canon warranty for refurbs is 90 days. A new camcorder is a year. The quality from this store is excellent/like new, so don't worry about that. The only visible difference is the packaging is generic. If you are concerned about only 90 days, you can buy a 3-year "Mack Warranty" for about $50 that also covers accidents. If you do, make sure it is purchased from an "authorized seller" as sites like Amazon and ebay have some independent sellers that aren't authorized. So, when someone goes to make a claim, they wouldn't honor it.
Adorama is an authorized Mack warranty seller and are on Amazon and their own site..

I think if you're willing to spend $400 then you might as well add the newer Canon M500 to your choices but it's true you'll spend more once you get a memory card.

Yes camcorders like the Panasonic V500 and the r series Canon's are to be avoided. They are very cheap because they are using very cheap components. A Panasonic recommendation would be the V700. A benefit of the V700 is higher still photo resolution, 1080 60p shooting mode and most likely a better stabilizer and as for the Canon M400/M500, you most likely get much better low light capabilities. I don't know about battery differences.