belfiglioval,
Believe it or not, you really don't need a 'dual-band' antenna. Having one certainly won't hurt, but it's not completely necessary to still cover both bands just fine. As 'SR385' said, height is the biggy.
What's with the "don't need a dual-band antenna" thingy? It sort of surprised me too, but it's a fact. I 'started' with a '7800 just like you are, lately, that is. Really started quite a few years ago with a different brand radio but quit VHF/UHF, liked HF better. Honestly didn't 'keep up' with any of the VHF/UHF stuff. Considering the radio I did start with, I'm surprised I ever got back into it again!
Long story, not worth hearing.
I just happen to have a neighbor who is sort of big into VHF/UHF stuff. He gave me a home made 2 meter 'J'-pole to sort of get me started (again). He said it worked just fine on '440 too. I thought, boy, does someone need their thinking re-adjusted a little. Turns out -I- was the one needing that re-thinking. It works just fine on both 2 meters and '440. Later, I got one of the 'Comet' "GP" series of base antennas. After doing some comparisons, that @#$ 2 meter 'J'-pole does as well as the more expensive 'Comet' (not the high-end model). Ain't that a hoot? There is a performance difference in the 'Comet's favor, but not a very big one. Considering the '7800's abilities, that difference isn't very 'bad' at all. A couple of radios later, still have/use the 'J'-pole, and the 'Comet', just not doing the same thing with both. Sort of dedicated the 'J'-pole and '7800 to one thing, the other radios to something else. (Another long story, not worth hearing unless you're into APRS stuff and making mistakes about things.)
So, depending on finances and antenna space available, there are certainly alternatives to high dollar VHF/UHF antennas.
I also agree with 'SR385' about the kind of feed line used. Look for something with low VHF/UHF losses. If the distance between radio/antenna isn't all that long, almost anything will 'work', some just better than others, strictly a matter of how far you have to go.
The biggy is antenna height above surrounding stuff! That's where you ought'a shoot for as much as you can afford.
- 'Doc