Ranges come in 24-inch, 30-inch (actually 29 & 7/8, 56 and so on. So, if the existing stove looks like a 30 inch, the a standard 30 inch will fit. If you have any questions, get the model numbers of your candidates for replacement and look for someplace to download the installation You want to make sure that the 240v instructions. is in the proper area.

All that being said, I suspect that finding a radiant smoothtop is going to be difficult when you arelooking for a price at or below $500. That you don't want to go scratch-n-dent (ding-n-bing) cna further complicate thigs
Everybody I know who bought an "inexpensive" smoothtop jad t spend a couple hundred above your budget for a smoothtop that was not dog slow and had an oven that heated

Can this wait until the next bg holiday sale (Columbs day?)

Otherwise, I would be inclied to look at coil burner models. Plain, simpe, durable, mare technology.relatively evenly. Also seem to have beeter (more even) ovens tan smoothop competitors. Frankly, I have no idea why coil burner stove seem to have beet ovens in the lower end of the price scale but, somehow, they do.

In that price range, I would be inclined to look for a coil burner unit. Plain, simple and (mostly) durable.It's mature technology. I would look at Hotpoint (a GE brand). For a about $550 you can get a Kenmore 90313 coil burner stove with convection oven. For about $450 you can get a Hotpoint which used to be Consumer Report's highest rated coil burner. (It will be more if you want it stainless.)

Wound up spending more than I anticipated or my son said would really be necessary...
he wanted a self cleaning oven with hidden element and cooktop with a power element...a power element is not found on range under 600
and a hidden heating element also adds to price
I read some negative reviews of the "steam cleaning" process so went with conventional style of self-cleaning...
I know some people don't have high ratings for that brand but read mostly positive reviews...

got it from Lowe's which has free delivery and take away of the old range..
Sears charges 70 for delivery and 10 to take away...
Ordered a Frigidaire LGEF3033KW
he did not really want a convection but that was bonus
On sale for 647 and change--
They seem to be pretty happy with it...Lowe's reviews were 12 of 13 very positive so hopeful it will be good unit for them...

Well shoot. If you're in southern california, they can have mine for $300. It is in pristine shape but didn't fit in with the kitchen remodel. It is currently sitting in the back porch waiting to be put on cr@igslist.

Not sure what you're going to find new for under $500. My new slide-in electric stove just cost $1700. Yikes!