The 26-year-old appeared almost 300 times for the Robins and scored 26 goals during close to nine years at the club.
Di Paola said: “He’s a good player. He’s got a lot of experience at this level.
"I think he’ll really fit into the group as he's a nice lad. He knows Danny Dudley (Hornets defender) quite well.
“He lives about 20 minutes outside Horsham and he was looking for a move away from the London area so it’s a good fit for us.
“He’s a bit of a winner. He wants to have success and he wants to do well, which is what we want to do as well.
“Hopefully he enjoys his time at Horsham and he can replace two popular members of the team in Steve Metcalf and Chris Sessegnon.
"Both were really well liked and not having them is a loss to the group. Hopefully Bobby can come in and fill that void.”
Price was Carshalton vice-captain in 2017-18 and helped them win the Isthmian South title
Di Paola said: “It’s nice having leaders. He’s 26 and he’s got mountains of experience. He’s been playing at the level below and this level now for eight years.
“It’s not like we’re taking an untried player and getting him up to speed. I feel he will hit the ground running and be a good part of the group.”
Price came through the Robins’ academy as a midfielder, before reverting to the full-back role, but Di Paola said he would be used in a defensive position.
He said: “I see him as a right-sided defender to be honest. I don’t think we’d end up playing him in midfield but it’s always useful.
“Bringing him in takes a bit of the pressure off as Sessegnon has moved on. It has killed that concern.
“I feel like we’ve brought a really good full-back into the club. It was a problem before Sess came in because Mets (Metcalf) had a few injuries.
"Sess came in and did really well for us. Hopefully Bobby can do the same.”
Di Paola said more incomings were in the offing and that more will be revealed in the coming weeks.
He added: “We’ve got two others that have signed and we’ve got another couple that will hopefully sign in the next week or so.
“There will be some announcements coming out prior to pre-season kicking off.”