Well, I would like to pick up some very small sound like: - Pressing Keyboard - Using the zipper - Scratch yourself
I don't have a lots of money to buy expensive equipment. How can I pick up these sounds with a small budget? (< 100 USD) Thanks.
look into brands like microphone madness etc. sometimes they repackage quality omni capsules (e.g. sennheiser mke2) for a lot cheaper due to them being slightly mismatched, or otherwise failing QC.
contact mics are another way to get some sounds - the character will be very specific and the cheaper the mics = the more EQ you'd need to apply, but the cheapest transducers are ridiculously cheap. brush up on your soldering skills.....
small omnis or contacts will allow you to get close, at the cost of somewhat limiting the character of sounds (sound needs at least a bit of space to develop), but you will rerecord these same sounds later when you get another chance.
stretch your budget to $150, the probability of finding a compromise goes higher. arm yourself with patience. if you're not money rich you need to be time rich for this to work. also i'm tired of plugging the $200-something pcm-m10 which has unexpectedly quiet built-in mics for the price.
a really quiet mic is out of reach, i'm afraid. these and their preamps combined easily get into the 4 digits budget.
For $100 you are really very limited. You can afford a cheap handheld recorder like the zoom H1 or possibly the tascam DR-05. These will work, but you will need to get the recorder fairly close to record quiet sources like you mention. You do get what you pay for with sound equipment, so don't expect miracles - you may get something useable for your purposes (whatever they are), but it will not be the kind of quality you would find in professionally recorded sound libraries.
A decent quality standard mic for picking up speaking costs $100 or more. You are not going to find a good microphone that has sufficiently low levels of noise to get a good recording for $100. You will also likely have a problem finding a good, quiet environment to do the recording in unless you already have a sound proofed studio space.
Recording quiet sounds requires three things, a highly sensitive mic with very low noise, a high quality pre-amp with low noise and a quiet space so that ambient noise doesn't overpower the sound you are trying to capture. A highly directional mic could help offset the background noise problem some, but again, you are still talking something well out of your price range (possibly even an order of magnitude higher).
http://www.freesound.org. Make sure any sounds you use are public domain though.
Cheap, OK quality: Samson Go Mic: $40.
Inexpensive, great quality: Monoprice Large Diaphragm Condenser Microphone $75, occasionally on sale for as low as $60.
The Samson Go Mic probably uses the same mic elements that Samson uses in their Zoom brand portable digital audio recorders. The Go Mic is a USB mic, so you don't need anything else to plug it in to a computer.
The Monoprice condenser is excellent, as Tape Op confirms. Unless you have a mixer or audio interface with preamps, you will also need a preamp that has phantom power. I'm using the ART Tube MP with an upgraded tube. This combination is much cleaner and more sensitive than the Samson, but will push the upper limit of your budget. Don't forget that you need an XLR cable and a mic stand too.
The Korg CM-100 and CM-200 contact mics are also nice to have around, I picked up several CM-100s when they were selling for about $10 each. They don't need phantom power, but definitely benefit from some preamp gain. The trim gain on my MOTU 828Mk2 is adequate, but now I find it easier to just work with the Monoprice mic.
If you have no ideas on sound equipment, get a linear PCM recorder. I made two recordings with TASCAM DR-05 (which is at about $100 I think, maybe a bit more expensive). I won't judge the quality of the sound, I only show what you get for the price paid.
(Disclaimer: I didn't fiddle much with the setup, neither the position nor the level, you can probably do better, and you can post-process the file at least with some basic noise reduction filter.)
IMHO, you won't get much better price-quality ratio than with some of these recorders. Their AD conversion seems to be pretty resonable and the microphone quality is worth the money.
Another option is a USB microphone, but the usage of it is limited by having another device with you which proved me to be a burden. It's much easier to operate with a battery-powered gadget than with something on a wire connected to a computer.
I'm assuming you have zero equipment already, so my suggestion would be some cheap shotgun which can be battery powered, so you could plug it directly to whatever you are using to record like computer or cell phone with some adapter.
Rode NTG-2 would be ok, but it's above your budget and even it won't do miracles without good preamp.
At least Thomann sells t.bone EM 9600, which is very cheap battery powered shotgun and would fit into your budget. I wouldn't expect miracles though, but you could probably get something useful out of it.
And the thing with very low volume recordings is as much about space as it's about equipment. You will need a very very quiet place to record the sounds and even after that there could be need for noise reduction. ReaFIR from Reaplugs suite and Audacitys noise reduction are some free options for that.
Anyway, if you plan to continue your sound design adventures I'd recommend skipping the t.bone and just getting NTG-2. It's great entry level shotgun and could serve you for years to come.