I've decided that I want to save the money I make at my internship this summer and buy a 6 string fretless. My friend has one that I fell in love with, and I'm looking to expand my range and my tone. I'm having some trouble finding a decent looking brand that's not super expensive, and I came across the LB76-F that's right around $1100 for the base model, which I would consider to be a reasonable price to pay for a decent instrument.

Has anyone had any experience with these basses? Would you recommend them or not? If not, do you have any suggestions for another 6-string fretless?

Thanks in advance.
carvin stuff is generally fairly high quality, you don't get away with spending the time, money and effort to build something in the US if it's not decent. the carvin basses i've had experience with are no exception to this and, in my opinion, are one of the stronger points of their lineup.

Their stuff (at least instruments anyway, not so much amps/other sound equip) is all custom made to order as well so if you're willing to drop some extra cash when buying new it opens up all kinds of extra options. As far as 6 string fretless you're going to have VERY few factory options.

IIRC warwick has a couple fretless 6s ('vette and thumb maybe others?) in their pro series lineup which tend to be an amazing value used if you can find them

I think i remember seeing a dean fretless priced cheap used at a shop on the other side of town ages ago, didn't sit down with it to check it out at the time though

MTD's kingston line is in that ballpark and offers quite a few options, i would be really surprised if they didn't offer a fretless 6

to my knowledge i don't know of any ibanez fretless 6s which is surprising considering how many 6s they make on the cheap

Also on the custom front you could go with a warmoth build, can save you a little or offer you more opportunity to add some personal touches depending on what all you're comfortable with doing (a finished body and neck can pretty much have some hardware slapped on and be bolted together and playing in short order if you're comfortable withing soldering/setup/etc)

anything else custom is likely to be a little steep.
I've got half a dozen Carvin guitars and an LB-75 (five-string) bass. Carvin's pretty well respected among bassists in general, and they're very well done. Mine's been bulletproof.