First, don't bother with the Spektrum. I don't want to call it "garbage", but I'd definitely avoid it. While their aerial radios are great, their surface radios are a bit on the "deficient" and "crippled" side. Futaba, on the other hand, is excellent. I don't have the 4PM...but, I do have the 7PX, and it is outstanding. Other than having three fewer channels, the 4PM has most of the same capabilities.
As mentioned by Spoo76, you should also consider FlySky. The GT3B GT3B was found to have its own collection of problems, and was replaced by the GT3C (as low as $52)...but, it's only a 3-channel. FlySky does make the GT5 (as low as $63, and a 6-channel), which not only has the additional channels you want/need, but doesn't cost much more than the GT3C (which I also have).
I purposely saved what could be the "best bang for three buck" for last...and, it's also by FlySky - the Noble NB4. Technically, it's a 4-channel...but, it's also a 12-channel. How? Through firmware updates. When originally released (2+ years ago), it only supported up to 4 channels (plus, it did have a number of problems, which have all been addressed/fixed through firmware updates). A later firmware update increased it to 8 channels (tho they hadn't yet released any 8-channel receivers). More recently, firmware was released that supports 12 channels...and, they released 8-channel & 12-channels receivers. The Noble NB4 sells for as little as $190 through Banggood, or $230 at most US hobby shops that carry it (Team Powers recently became the official US distributor, enabling a LOT of LHSs to start carrying FlySky).
For that $230, you get the Tx, two 4-channel Rx, the USB cable (for updating firmware, for exporting/imprint saved model data, and...get ready for this, as it's truly amazing (and one-of-a-kind)...for using the NB4 as aPC game controller. While the GT3B/C and GT5 are entirely plastic, the NB4 is a mix of plastic & aluminum...FAR more sturdy than the other FlySky offerings (except for the just-released Noble Pro, but it's $380). While FlySky's other offerings are "good", they've still felt somewhat 'flimsy'...almost "toy like". The Noble NB4 (and Pro) feel like top-of-the-line products, equal in build quality to the best offerings made by Futaba, Spektrum, and Sanwa/Airtronics. I would HIGHLY suggest checking into, and reading up on, the FlySky Noble NB4. I will also mention that, in addition to the Futaba 7PX & Flight GT3C, I also have the FlySky Noble NB4.
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