IMHO, it is not just what microphone you use, but also how you use it. Even cheap RadioShack mics can sound acceptable if used correctly. I generally use one of two setups for recording my orchestras and brass band. One is the spaced omni method and the other is a near coincident hypercardioid method. In either case, one needs space between the instruments and the mics. If possible, use a large room or better yet, a small theatre.
If using the spaced omni method (potentialy the simplest and best sound for the least money), place the omnidirectional microphones on stands six to twelve feet off the ground (or hang them from the ceiling) and about 10 to 12 feet in front of the trumpet or six feet or so in front of the front row of the ensemble being recorded. Space them about 4 to 8 feet from the centerline of the group. Set the gain of your recorder so that the loudest passages don't go above about -3dB if you are using a digital recorder, or above +3dB if using an analog recorder. DAT recorders are highly recommended because they lack audible wow and flutter, as well as having the greatest dynamic range.
You will likely also need a microphone preamplifier, since many recorders don't include them anymore. For quickie recordings, I use my Sony D-3 DAT recorder (which does have mic inputs) with a pair of matching transformers to couple the microphones to the DAT. If I use my Tascam DA-30 II recorder, I have to use an external preamplifier. You may have an old cassette recorder that has a pair of mic inputs, in which case, you may be able to use it as a preamp , and connect it's line output to the line input of the DAT recorder.
I use either Nakamichi CM-300 mics with the CP-1 omni capsules or some onmi mics I built using those inexpensive Panasonic omni mic capsules you see advertised in the hobbyist magazines.
Another possible technique is to use the RadioShack PZM microphones (the ones on the black square metal plate). They are like omni mics but are designed to be placed on a large flat surface like the floor. Place them where I suggested placing the omnis, but directly on the floor. I have used mine a few times and was fairly pleased with the results.
The other method is one in which a pair of directional (cardioid or hypercardioid) mics are mounted in a "V" configuration on a single stand directly in back of the conductor (maybe 6 feet in back and 12 feet high is how I do it). This method simulates the way our ears hear and the recording, if played back over headphones, sounds incredibly lifelike, but the stereo seperation is not as good as with the spaced omni technique when played back over speakers, IMHO. I either use my Nakamichis with the CP-2 cardioid capsules or the TOA-KY mics I got a couple of years ago, depending upon my mood, and if I have AC power for my good microphone preamp and thus phantom power for the KYs.
This is more info than you probably wanted, but I wanted to be sure you and everyone else knows that it is not so much the equipment, as how it is used. (kinda like the trumpet, isn't it?!)
Hope this helps!