My first question to you would be, "what will you use the gun for?"
Since I don't know, I'll answer as best I can.
I have two H&R single shots in 20 gauge (a Pardner and a Topper). They are fun to shoot, and even if you don't get one as your first gun, I'd recommend getting one eventually just for the fun of it.
There are several types of Toppers. Current production models include:
Topper: most basic, no recoil pad, no interchangeable chokes, no vent rib, weighs 5-6 pounds*
Topper Deluxe: has recoil pad and interchangeable chokes, but no vent rib, weighs 6-3/4 pounds*
Topper Deluxe Classic: has recoil pad, interchangeable chokes, and vent rib, weighs 6 to 7 pounds*
*weights based on catalog listing
The basic Topper model with its feathery weight an lack of a recoil pad will rattle your teeth a bit. If that's what you're considering, I'd say an aftermarket recoil pad is almost a must (this will add $20-30 to the overall expense though).
Either of the higher end Topper models would probably be comfortable enough provided you aren't shooting many magnum shells or slugs. I personally can shoot better with a gun that has a vent rib versus one with a plain barrel, but that's just a matter of preference.
So, without actually knowing what you intend do do with the gun, I'll just go from my own experience and say the basic Topper model may be worth $90, the Topper Deluxe is very likely worth $90, and the Topper Deluxe Classic is definitely worth $90.
[edited to add] I concur with lamarw's comments about a single shot teaching good habits to a new shooter. I started with a pump shotgun, and I initially learned to shoot really fast but not very accurately. Going to a single shot later on forced me to be more conscious of what I was doing.