I'm looking to start recording my own field recordings, effects, and foley for a portfolio. What type of mics are used for this? Shotgun? Does anyone recommend any specific affordable mics to start doing this?
For Foley Usually LDCs (large diaphragm condensors) since of prime importance, they retain a lower noise floor. U87s are often used for this, sometimes with an MKH 416 or KM81/82 as a room mic. Octava makes a good LDC I've used, although I cannot recall the model number - it's cylinder-looking one. AT2035 would more in the bargain range.
For FX, it can be LDCs, dynamic mics (like MD421, SM58, RE20 <- great mic by the way), and most often out in the field it'll be SDCs like shotguns and small-capsule mics (like the Schoeps CMC+MK41 or CCM4, Senn MKH 8040, Neumann KM184, or Studio Projects C4)
Although as I've learned the hard way, you really do get what you pay for in a mic. AT tends to have a pretty good track record for the bargain territory however, same with the Sennheiser ME series. The top end mics (at least as far as effects recording go) are usually going to be from the Sennheiser MKH/8000 series, Neumman KM and U series, Sanken CS series, DPA 4000 series (like the 4011) and Schoeps CMC/CCM sets. That's not to say you have to go all out, but it's wroth shopping around I think and possibly even waiting for something that's not in a dirt-cheap bargain territory. Usually a decent, workhorse mic will set you back about $1000-1200, but some decent ones can be had for the $500 range.
As far as start out with FX recording, I recommend a SDC capsule mic or shotgun because it can be portable in a modular windjammer like Rycote, and cardiod is probably the best pattern to begin with - other pickup patterns have specific, and usually somewhat limited, niche uses like bi-direction (often reserved for Mid-Side, Double MS, and Blumlein arrays) and Omni (often used with parabolic setups or as part of an AB spaced pair). Cardiod, on the other hand, is very versatile for recording hard FX without being too broad or narrow of a rejection axis.
As far as for recording ambience, that's going to require two mics minimum (or a dual capsule setup like the NT4). So this is one consideration to make as well - because what you decide for your starter mic will determine your recording limitations.
This is in large part why I've decided to go with a Mid Side setup myself - offers a direct mono signal, but also an adjustable stereo image (all the way into the mastering process, no less) all in one convenient windjammer. The caveat to this is you'll either pay between $1800-2400 for a "pre-built MS" mic like the Sanken CSS-5, or you'll have to buy both a cardiod and bi-direction mic to build a custom array and the proper windjammer moun to ensure phase coherence of the capsules. Which, depending upon your mic choices, can run you upwards of $3000 to build an entire MS kit "from mic to pistol grip".
Hopefully this wasn't too confusing! Buying your first mic should always be a fun experience, so always keep that in mind at the end of the day. Try renting or borrow some of them if you can, see what your ears respond to - at the end of the day what sounds good is good. Mic selection is also a very personal, subjective process to each individual and their tastes and sensibilities, so don't let anyone force you into a purchase - yet recommendations and experience from others can definitely be a helpful asset to weigh into the decision-making process (ex: in the past I haven't been fond of the Schoeps sound personally, but others love them and to each their own - maybe one ay I'll come around if I like what I hear sometime in a future audition and I'm open to it, but that's just where I stand right now). These are just musing from my own experience, to be taken worth a grain of salt. Good luck!
I usually use the Scheops CMC 6 mk4 or the Sennheiser 416. I have used wide diaphragm mics in the past the Neumanns and AKG's are also good. You need to check the transient response on any mic you use when doing foley because of the different kinds of sounds you are making.
I always stay away from "cheap" mic's because of the lack of good frequency response and noise floor. A foley stage needs to be really quiet with some room but generally it is a quieter space to let's say a music recording studio or a mixing studio.
Good luck though.