This is the one I saw that I kinda liked Wilson Electronics 12-inch Dual Band Magnet-Mount Antenna w/ SMA Male Connector
https://www.amazon.com/dp/B00KY4Q7DG/ref=cm_sw_r_cp_api_i_dGH.AbZN04GN4,
That's a cellular antenna. It should work well for 700 and 800, and likely it's long enough to give decent performance on UHF, it's not going to be a great performer on VHF.
Plus it's Wilson, which I can tell you from personal experience, sucks. I had a Wilson amp in one of my old trucks. The amp worked well enough, but the cheap antenna they sent with it fell apart first time I tried to pull it off the truck. I replaced it with a proper NMO permanent mount with a well designed cellular antenna.
How does a 700/800 MHz antenna effect my reception of a 400 MHz analog signal? Would I be missing a significant amount of traffic?
Depends on a number of variables, so no one is going to be able to tell you for sure.
-How strong are the signals you are trying to receive? A mismatched antenna is going to make things worse, maybe even allowing nearby cellular base stations to overload the front end of your scanner.
-Depends on the exact antenna. The design will dictate a lot. Ideally you do need an antenna that is resonate on the frequencies you want to listen to. Trying to use a cellular or 700/800MHz antenna and expecting it to work well on UHF and VHF is likely going to lead to disappointment. You can easily do better.
I’m looking for an inexpensive magnetic mount antenna for my vehicle, I prefer SMA connector type for my BCD436/BCD396 cause that would be the easiest/lower loss. I would like a wideband antenna but have have yet to find anything. I am mainly monitoring 700/800 MHz P25 Trunked systems with the exception of a few analog 400 band analog systems and one 150 MHz P25 trunked system.
…….
like I said I’m just looking for something inexpensive that I can toy around with until I get another vehicle that I am more interested into spending a lot of money on a more expensive antenna that I can hard mount. Not super concerned with how low quality the cable would be or anything.
Unless money is tight right now, you'd be better off just purchasing the right antenna and a mag mount. That way you can just move the antenna over to the new car when you have the mount installed. No reason to spend money on a cheap antenna now and then go out and buy a better one later. Just get the right stuff now.
Stick with NMO mounts. That'll give you the widest selection of antennas to choose from. It's the de-facto standard in the professional 2 way radio industry.
An NMO magnetic mount base with SMA connector:
Chrome:
https://www.theantennafarm.com/catalog/laird-technologies-gm8smi-7512
Black:
https://www.theantennafarm.com/catalog/pctel-maxrad-bgmsmai-4524
Both are $29.95. Maybe a bit more than you wanted to spend, but it's the right mount for the temporary installation, and you can always use it later on.
A multi-band antenna designed for the frequencies you want to listen to:
https://www.theantennafarm.com/catalog/larsen-nmo150-450-800-1050
$29.95. A known good antenna made by a reputable company that stands behind their product. It can easily be transferred over to your new car. It's designed to work on the VHF, UHF and 800MHz band, and will work just fine on the upper end of the 700MHz band where the stuff is you want to hear.
And, it'll likely outlast your car. I've got 20-30 year old Larsen antennas that are still going strong.
I know you want to keep the price down, but getting the right antenna should be your main goal. Cellular antennas will work fine for 700-800 and likely UHF, depending on the exact style, but will likely perform poorly on VHF. Getting the right gear now will save you money in the long run.