It is kind of hard to depend on what they have in stock but, I saw a nice pipe frame one like you are wanting with heavy duty wheels for a ridiculously low price at Sams Warehouse...2 days after I bought one for the same price of a much cheaper plastic build at home depot...

I'd definitely prefer pneumatic tires to the rigid wheels found on a most of convertibles.

Tractor Supply would be another good place to look.

I've purchased a couple of the afore-mentioned "pipe-frame" hand trucks from HD at decent prices. They have pneumatic tires, but no inner tubes :( so they kept losing air. I took them both to a local "wheel & caster" store and they were able to put inner tubes in them for a very good price. Now I have no flat tires even under ridiculously heavy loads. And it's convertible in that you can pull a pin and repostion the handle so that the truck is horizontal ("cart") rather than vertical.
This past weekend I put a big ol' Ramsa 8-bus on it and it didn't even flinch. Then I stacked my Bandmaster Reverb piggy-back monster, (3) guitar cases, plus a pedalboard onto it and pulled it over a quarter mile (!) on a gravel road to a blues gig. If I did that with one of those little "gig carts" I USED to have, they'd have gotten bent frames and the little wheels would have never navigated the rough terrain.

I like the pneumatic tires but the hard rubber wheels are more consistent. I'm not going to pull much across that much gravel anyhow. You can't make me. I won't do it. If you get pneumatic tires make sure you get a metal rim. I'm using pneumatic but I have to check air pressure before each job. I see some real nice gig racks but they weren't what I would call affordable. Of course tanks are not affordable.

Sally Hansen hard as nails
Mx. Remy Ann David

Here is a really good ($$$) one:

[="http://www.uline.com/BL_1835/Magliner-Aluminum-Convertible-Hand-Trucks"]Magliner Aluminum Convertible Hand Trucks[/]="http://www.uline.co…"]Magliner Aluminum Convertible Hand Trucks[/]

Here is one that will workk, for a lot less money:

[[url=http://="http://www.homedepo…"]800 Lb. Capacity Convertible Hand Truck - CHT800P at The Home Depot[/]="http://www.homedepo…"]800 Lb. Capacity Convertible Hand Truck - CHT800P at The Home Depot[/]

I have a Magliner. I've replaced the smaller top wheels a couple of times in it's life. It will go across grassy fields when necessary although I recommend looping a pull rope on the frame when in four wheel mode as a come-along. I've bent it up and straightened a couple of times too. But then nothing is Marine proof ^_^ (if it absolutely positively has to be destroyed overnight!)

800 Lb. Capacity Convertible Hand Truck - CHT800P at The Home Depot
That's mine!!! And the Magliner dealer was the shop that installed inner tubes in those tires. Do that and the HD truck is the BEST value you can get.

I've got one of these. Has worked pretty well for some decent loads for the last year and a half. Gotta check tires each time, but other than that, no problems.

[[url=http://[/URL]="http://accessories…"]Buy Rock n Roller R6 Mini Cart | Carts, Casters & Dollies | Musician's Friend[/]="http://accessories…"]Buy Rock n Roller R6 Mini Cart | Carts, Casters & Dollies | Musician's Friend[/]

I went to 4 stores looking for one of the aluminum lightweight folding wheels kind. Finally Lowes had them for $30 each which was a great deal. At that price I got 2...